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 $64.57   11.457%   $71.9678   $71.97   $71.95   $72.00  
  Purchase #2 $189.78   4.116%   $197.5913   $197.59   $197.60   $197.60  
  Purchase #3 $199.81   3.477%   $206.7574   $206.76   $206.75   $206.80  
  Purchase #4 $135.65   3.340%   $140.1807   $140.18   $140.20   $140.20  
  Purchase #5 $113.37   9.584%   $124.2354   $124.24   $124.25   $124.20  
  Purchase #6 $46.61   11.513%   $51.9762   $51.98   $52.00   $52.00  
  Purchase #7 $147.45   7.581%   $158.6282   $158.63   $158.65   $158.60  
  7 purchase totals = $897.24       $951.3370   $951.35   $951.40   $951.40