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 $65.69   11.522%   $73.2588   $73.26   $73.25   $73.30  
  Purchase #2 $154.82   9.561%   $169.6223   $169.62   $169.60   $169.60  
  Purchase #3 $241.27   8.108%   $260.8322   $260.83   $260.85   $260.80  
  Purchase #4 $12.37   11.738%   $13.822   $13.82   $13.80   $13.80  
  Purchase #5 $104.29   8.381%   $113.0305   $113.03   $113.05   $113.00  
  Purchase #6 $93.78   9.275%   $102.4781   $102.48   $102.50   $102.50  
  Purchase #7 $25.59   10.318%   $28.2304   $28.23   $28.25   $28.20  
  7 purchase totals = $697.81       $761.2743   $761.27   $761.30   $761.20