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 $51.69   5.653%   $54.612   $54.61   $54.60   $54.60  
  Purchase #2 $101.88   6.447%   $108.4482   $108.45   $108.45   $108.40  
  Purchase #3 $182.97   8.806%   $199.0823   $199.08   $199.10   $199.10  
  Purchase #4 $163.97   3.358%   $169.4761   $169.48   $169.50   $169.50  
  Purchase #5 $73.56   6.733%   $78.5128   $78.51   $78.50   $78.50  
  Purchase #6 $53.32   12.680%   $60.081   $60.08   $60.10   $60.10  
  Purchase #7 $136.98   6.315%   $145.6303   $145.63   $145.65   $145.60  
  7 purchase totals = $764.37       $815.8427   $815.84   $815.90   $815.80