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 $59.84   11.130%   $66.5002   $66.50   $66.50   $66.50  
  Purchase #2 $7.75   8.474%   $8.4067   $8.41   $8.40   $8.40  
  Purchase #3 $94.35   4.507%   $98.6024   $98.60   $98.60   $98.60  
  Purchase #4 $42.99   10.418%   $47.4687   $47.47   $47.45   $47.50  
  Purchase #5 $198.43   3.162%   $204.7044   $204.70   $204.70   $204.70  
  Purchase #6 $90.47   12.227%   $101.5318   $101.53   $101.55   $101.50  
  Purchase #7 $221.44   7.689%   $238.4665   $238.47   $238.45   $238.50  
  7 purchase totals = $715.27       $765.6807   $765.68   $765.65   $765.70