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 $229.40   5.468%   $241.9436   $241.94   $241.95   $241.90  
  Purchase #2 $155.57   11.763%   $173.8697   $173.87   $173.85   $173.90  
  Purchase #3 $75.93   9.867%   $83.422   $83.42   $83.40   $83.40  
  Purchase #4 $219.46   3.782%   $227.76   $227.76   $227.75   $227.80  
  Purchase #5 $202.38   13.570%   $229.843   $229.84   $229.85   $229.80  
  Purchase #6 $26.63   3.364%   $27.5258   $27.53   $27.55   $27.50  
  Purchase #7 $35.86   10.268%   $39.5421   $39.54   $39.55   $39.50  
  7 purchase totals = $945.23       $1,023.9062   $1,023.90   $1,023.90   $1,023.80