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 $46.88   13.734%   $53.3185   $53.32   $53.30   $53.30  
  Purchase #2 $57.77   8.865%   $62.8913   $62.89   $62.90   $62.90  
  Purchase #3 $234.33   4.252%   $244.2937   $244.29   $244.30   $244.30  
  Purchase #4 $193.28   6.730%   $206.2877   $206.29   $206.30   $206.30  
  Purchase #5 $40.73   13.154%   $46.0876   $46.09   $46.10   $46.10  
  Purchase #6 $8.43   7.315%   $9.0467   $9.05   $9.05   $9.00  
  Purchase #7 $162.97   13.602%   $185.1372   $185.14   $185.15   $185.10  
  7 purchase totals = $744.39       $807.0627   $807.07   $807.10   $807.00