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 $54.73   13.540%   $62.1404   $62.14   $62.15   $62.10  
  Purchase #2 $243.60   8.776%   $264.9783   $264.98   $265.00   $265.00  
  Purchase #3 $146.78   4.373%   $153.1987   $153.20   $153.20   $153.20  
  Purchase #4 $40.57   5.231%   $42.6922   $42.69   $42.70   $42.70  
  Purchase #5 $178.51   10.553%   $197.3482   $197.35   $197.35   $197.30  
  Purchase #6 $95.37   10.365%   $105.2551   $105.26   $105.25   $105.30  
  Purchase #7 $95.37   11.141%   $105.9952   $106.00   $106.00   $106.00  
  7 purchase totals = $854.93       $931.6081   $931.62   $931.65   $931.60