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 $92.87   5.718%   $98.1803   $98.18   $98.20   $98.20  
  Purchase #2 $13.72   11.841%   $15.3446   $15.34   $15.35   $15.30  
  Purchase #3 $51.81   3.602%   $53.6762   $53.68   $53.70   $53.70  
  Purchase #4 $143.98   12.128%   $161.4419   $161.44   $161.45   $161.40  
  Purchase #5 $96.76   4.650%   $101.2593   $101.26   $101.25   $101.30  
  Purchase #6 $230.27   8.160%   $249.06   $249.06   $249.05   $249.10  
  Purchase #7 $98.85   8.742%   $107.4915   $107.49   $107.50   $107.50  
  7 purchase totals = $728.26       $786.4538   $786.45   $786.50   $786.50