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 $74.54   3.209%   $76.932   $76.93   $76.95   $76.90  
  Purchase #2 $9.76   4.121%   $10.1622   $10.16   $10.15   $10.20  
  Purchase #3 $195.54   7.782%   $210.7569   $210.76   $210.75   $210.80  
  Purchase #4 $188.31   9.368%   $205.9509   $205.95   $205.95   $206.00  
  Purchase #5 $67.27   8.668%   $73.101   $73.10   $73.10   $73.10  
  Purchase #6 $225.90   10.474%   $249.5608   $249.56   $249.55   $249.60  
  Purchase #7 $119.27   6.800%   $127.3804   $127.38   $127.40   $127.40  
  7 purchase totals = $880.59       $953.8442   $953.84   $953.85   $954.00