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 $208.27   9.726%   $228.5263   $228.53   $228.55   $228.50  
  Purchase #2 $146.52   7.198%   $157.0665   $157.07   $157.05   $157.10  
  Purchase #3 $66.56   13.367%   $75.4571   $75.46   $75.45   $75.50  
  Purchase #4 $98.28   7.328%   $105.482   $105.48   $105.50   $105.50  
  Purchase #5 $149.99   12.126%   $168.1778   $168.18   $168.20   $168.20  
  Purchase #6 $53.99   10.626%   $59.727   $59.73   $59.75   $59.70  
  Purchase #7 $124.66   6.714%   $133.0297   $133.03   $133.05   $133.00  
  7 purchase totals = $848.27       $927.4664   $927.48   $927.55   $927.50