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 $58.84   12.541%   $66.2191   $66.22   $66.20   $66.20  
  Purchase #2 $245.39   8.352%   $265.885   $265.89   $265.90   $265.90  
  Purchase #3 $90.35   4.308%   $94.2423   $94.24   $94.25   $94.20  
  Purchase #4 $196.62   10.471%   $217.2081   $217.21   $217.20   $217.20  
  Purchase #5 $135.84   12.234%   $152.4587   $152.46   $152.45   $152.50  
  Purchase #6 $35.63   9.256%   $38.9279   $38.93   $38.95   $38.90  
  Purchase #7 $103.86   6.206%   $110.3056   $110.31   $110.30   $110.30  
  7 purchase totals = $866.53       $945.2467   $945.26   $945.25   $945.20