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 $55.33   11.234%   $61.5458   $61.55   $61.55   $61.50  
  Purchase #2 $58.61   13.540%   $66.5458   $66.55   $66.55   $66.50  
  Purchase #3 $250.99   6.669%   $267.7285   $267.73   $267.75   $267.70  
  Purchase #4 $122.62   12.781%   $138.2921   $138.29   $138.30   $138.30  
  Purchase #5 $195.27   9.302%   $213.434   $213.43   $213.45   $213.40  
  Purchase #6 $7.26   3.793%   $7.5354   $7.54   $7.55   $7.50  
  Purchase #7 $178.69   12.700%   $201.3836   $201.38   $201.40   $201.40  
  7 purchase totals = $868.77       $956.4652   $956.47   $956.55   $956.30