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 $227.47   7.369%   $244.2323   $244.23   $244.25   $244.20  
  Purchase #2 $106.87   11.513%   $119.1739   $119.17   $119.15   $119.20  
  Purchase #3 $244.75   8.263%   $264.9737   $264.97   $264.95   $265.00  
  Purchase #4 $119.89   10.609%   $132.6091   $132.61   $132.60   $132.60  
  Purchase #5 $67.27   9.259%   $73.4985   $73.50   $73.50   $73.50  
  Purchase #6 $193.91   13.551%   $220.1867   $220.19   $220.20   $220.20  
  Purchase #7 $174.26   4.608%   $182.2899   $182.29   $182.30   $182.30  
  7 purchase totals = $1,134.42       $1,236.9641   $1,236.96   $1,236.95   $1,237.00