Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $111.82   13.570%   $126.994   $126.99   $127.00   $127.00  
  Purchase #2 $190.52   8.460%   $206.638   $206.64   $206.65   $206.60  
  Purchase #3 $238.79   7.130%   $255.8157   $255.82   $255.80   $255.80  
  Purchase #4 $48.84   10.114%   $53.7797   $53.78   $53.80   $53.80  
  Purchase #5 $149.49   5.240%   $157.3233   $157.32   $157.30   $157.30  
  Purchase #6 $196.78   6.771%   $210.104   $210.10   $210.10   $210.10  
  Purchase #7 $107.86   8.279%   $116.7897   $116.79   $116.80   $116.80  
  7 purchase totals = $1,044.10       $1,127.4444   $1,127.44   $1,127.45   $1,127.40