How about something like this?

use strict;
use warnings;
use Data::Dumper;

my %totals;
for (1 .. 10) {
    my @plus = (1, 2, 3);
    @totals{qw(a b c)} = map { $_ + shift @plus } @totals{qw(a b c)};
}
print Dumper \%totals;
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The map will add the first element of @plus to each element of the slice in order. However, since the first element gets shifted, $totals{a} gets incremented by 1, $totals{b} by 2 and $totals{c} by 3.