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 $233.26   10.167%   $256.9755   $256.98   $257.00   $257.00  
  Purchase #2 $163.71   12.590%   $184.3211   $184.32   $184.30   $184.30  
  Purchase #3 $230.72   3.476%   $238.7398   $238.74   $238.75   $238.70  
  Purchase #4 $146.27   9.381%   $159.9916   $159.99   $160.00   $160.00  
  Purchase #5 $227.75   3.574%   $235.8898   $235.89   $235.90   $235.90  
  Purchase #6 $85.50   9.772%   $93.8551   $93.86   $93.85   $93.90  
  Purchase #7 $169.74   7.321%   $182.1667   $182.17   $182.15   $182.20  
  7 purchase totals = $1,256.95       $1,351.9396   $1,351.95   $1,351.95   $1,352.00