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 $125.95   11.382%   $140.2856   $140.29   $140.30   $140.30  
  Purchase #2 $20.64   10.330%   $22.7721   $22.77   $22.75   $22.80  
  Purchase #3 $54.70   13.730%   $62.2103   $62.21   $62.20   $62.20  
  Purchase #4 $169.52   7.485%   $182.2086   $182.21   $182.20   $182.20  
  Purchase #5 $215.84   9.791%   $236.9729   $236.97   $236.95   $237.00  
  Purchase #6 $210.33   9.639%   $230.6037   $230.60   $230.60   $230.60  
  Purchase #7 $82.99   5.243%   $87.3412   $87.34   $87.35   $87.30  
  7 purchase totals = $879.97       $962.3944   $962.39   $962.35   $962.40