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 $22.70   10.180%   $25.0109   $25.01   $25.00   $25.00  
  Purchase #2 $170.83   3.556%   $176.9047   $176.90   $176.90   $176.90  
  Purchase #3 $60.71   8.669%   $65.9729   $65.97   $65.95   $66.00  
  Purchase #4 $237.61   8.788%   $258.4912   $258.49   $258.50   $258.50  
  Purchase #5 $58.74   5.754%   $62.1199   $62.12   $62.10   $62.10  
  Purchase #6 $240.82   11.466%   $268.4324   $268.43   $268.45   $268.40  
  Purchase #7 $194.35   8.211%   $210.3081   $210.31   $210.30   $210.30  
  7 purchase totals = $985.76       $1,067.2401   $1,067.23   $1,067.20   $1,067.20