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 $205.75   4.729%   $215.4799   $215.48   $215.50   $215.50  
  Purchase #2 $85.93   10.862%   $95.2637   $95.26   $95.25   $95.30  
  Purchase #3 $26.55   11.364%   $29.5671   $29.57   $29.55   $29.60  
  Purchase #4 $60.62   7.870%   $65.3908   $65.39   $65.40   $65.40  
  Purchase #5 $151.56   10.368%   $167.2737   $167.27   $167.25   $167.30  
  Purchase #6 $131.90   13.315%   $149.4625   $149.46   $149.45   $149.50  
  Purchase #7 $215.96   9.567%   $236.6209   $236.62   $236.60   $236.60  
  7 purchase totals = $878.27       $959.0586   $959.05   $959.00   $959.20