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 $28.99   11.548%   $32.3378   $32.34   $32.35   $32.30  
  Purchase #2 $104.67   8.221%   $113.2749   $113.27   $113.25   $113.30  
  Purchase #3 $204.71   5.682%   $216.3416   $216.34   $216.35   $216.30  
  Purchase #4 $30.57   11.733%   $34.1568   $34.16   $34.15   $34.20  
  Purchase #5 $99.53   11.821%   $111.2954   $111.30   $111.30   $111.30  
  Purchase #6 $26.52   6.803%   $28.3242   $28.32   $28.30   $28.30  
  Purchase #7 $236.38   12.750%   $266.5185   $266.52   $266.50   $266.50  
  7 purchase totals = $731.37       $802.2492   $802.25   $802.20   $802.20