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 $88.90   4.583%   $92.9743   $92.97   $92.95   $93.00  
  Purchase #2 $185.34   10.214%   $204.2706   $204.27   $204.25   $204.30  
  Purchase #3 $77.86   7.177%   $83.448   $83.45   $83.45   $83.40  
  Purchase #4 $178.53   8.177%   $193.1284   $193.13   $193.15   $193.10  
  Purchase #5 $249.78   5.227%   $262.836   $262.84   $262.85   $262.80  
  Purchase #6 $52.94   8.248%   $57.3065   $57.31   $57.30   $57.30  
  Purchase #7 $140.43   3.147%   $144.8493   $144.85   $144.85   $144.80  
  7 purchase totals = $973.78       $1,038.8131   $1,038.82   $1,038.80   $1,038.70