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 $238.98   10.667%   $264.472   $264.47   $264.45   $264.50  
  Purchase #2 $31.78   8.393%   $34.4473   $34.45   $34.45   $34.40  
  Purchase #3 $49.79   8.724%   $54.1337   $54.13   $54.15   $54.10  
  Purchase #4 $43.50   6.184%   $46.19   $46.19   $46.20   $46.20  
  Purchase #5 $107.38   11.411%   $119.6331   $119.63   $119.65   $119.60  
  Purchase #6 $97.62   4.790%   $102.296   $102.30   $102.30   $102.30  
  Purchase #7 $90.37   8.281%   $97.8535   $97.85   $97.85   $97.90  
  7 purchase totals = $659.42       $719.0256   $719.02   $719.05   $719.00