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 $192.99   13.472%   $218.9896   $218.99   $219.00   $219.00  
  Purchase #2 $32.35   8.252%   $35.0195   $35.02   $35.00   $35.00  
  Purchase #3 $173.51   12.778%   $195.6811   $195.68   $195.70   $195.70  
  Purchase #4 $56.63   13.787%   $64.4376   $64.44   $64.45   $64.40  
  Purchase #5 $91.30   4.191%   $95.1264   $95.13   $95.15   $95.10  
  Purchase #6 $49.78   11.207%   $55.3588   $55.36   $55.35   $55.40  
  Purchase #7 $75.40   4.598%   $78.8669   $78.87   $78.85   $78.90  
  7 purchase totals = $671.96       $743.4799   $743.49   $743.50   $743.50