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 $169.44   7.524%   $182.1887   $182.19   $182.20   $182.20  
  Purchase #2 $131.41   11.259%   $146.2055   $146.21   $146.20   $146.20  
  Purchase #3 $169.98   11.312%   $189.2081   $189.21   $189.20   $189.20  
  Purchase #4 $59.94   11.690%   $66.947   $66.95   $66.95   $66.90  
  Purchase #5 $156.79   7.792%   $169.0071   $169.01   $169.00   $169.00  
  Purchase #6 $139.59   4.683%   $146.127   $146.13   $146.15   $146.10  
  Purchase #7 $51.28   6.757%   $54.745   $54.75   $54.75   $54.70  
  7 purchase totals = $878.43       $954.4284   $954.45   $954.45   $954.30