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 $83.73   12.689%   $94.3545   $94.35   $94.35   $94.40  
  Purchase #2 $114.82   5.622%   $121.2752   $121.28   $121.30   $121.30  
  Purchase #3 $76.55   8.806%   $83.291   $83.29   $83.30   $83.30  
  Purchase #4 $163.77   5.401%   $172.6152   $172.62   $172.60   $172.60  
  Purchase #5 $149.48   8.735%   $162.5371   $162.54   $162.55   $162.50  
  Purchase #6 $210.53   10.457%   $232.5451   $232.55   $232.55   $232.50  
  Purchase #7 $71.29   5.163%   $74.9707   $74.97   $74.95   $75.00  
  7 purchase totals = $870.17       $941.5888   $941.60   $941.60   $941.60