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 $171.43   6.599%   $182.7427   $182.74   $182.75   $182.70  
  Purchase #2 $110.63   9.763%   $121.4308   $121.43   $121.45   $121.40  
  Purchase #3 $95.64   6.633%   $101.9838   $101.98   $102.00   $102.00  
  Purchase #4 $80.34   6.644%   $85.6778   $85.68   $85.70   $85.70  
  Purchase #5 $153.64   10.545%   $169.8413   $169.84   $169.85   $169.80  
  Purchase #6 $245.53   6.421%   $261.2955   $261.30   $261.30   $261.30  
  Purchase #7 $48.41   5.735%   $51.1863   $51.19   $51.20   $51.20  
  7 purchase totals = $905.62       $974.1582   $974.16   $974.25   $974.10