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 $67.59   8.675%   $73.4534   $73.45   $73.45   $73.50  
  Purchase #2 $190.78   10.494%   $210.8005   $210.80   $210.80   $210.80  
  Purchase #3 $225.38   10.781%   $249.6782   $249.68   $249.70   $249.70  
  Purchase #4 $20.42   11.417%   $22.7514   $22.75   $22.75   $22.80  
  Purchase #5 $123.93   13.510%   $140.6729   $140.67   $140.65   $140.70  
  Purchase #6 $13.92   3.636%   $14.4261   $14.43   $14.45   $14.40  
  Purchase #7 $91.88   7.602%   $98.8647   $98.86   $98.85   $98.90  
  7 purchase totals = $733.90       $810.6472   $810.64   $810.65   $810.80