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 $244.40   11.856%   $273.3761   $273.38   $273.40   $273.40  
  Purchase #2 $125.59   4.578%   $131.3395   $131.34   $131.35   $131.30  
  Purchase #3 $33.56   9.563%   $36.7693   $36.77   $36.75   $36.80  
  Purchase #4 $52.62   4.575%   $55.0274   $55.03   $55.05   $55.00  
  Purchase #5 $63.76   4.117%   $66.385   $66.39   $66.40   $66.40  
  Purchase #6 $149.44   8.326%   $161.8824   $161.88   $161.90   $161.90  
  Purchase #7 $62.80   11.676%   $70.1325   $70.13   $70.15   $70.10  
  7 purchase totals = $732.17       $794.9122   $794.92   $795.00   $794.90