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 $89.40   6.808%   $95.4864   $95.49   $95.50   $95.50  
  Purchase #2 $152.96   10.223%   $168.5971   $168.60   $168.60   $168.60  
  Purchase #3 $68.78   10.844%   $76.2385   $76.24   $76.25   $76.20  
  Purchase #4 $165.39   6.626%   $176.3487   $176.35   $176.35   $176.30  
  Purchase #5 $131.70   7.361%   $141.3944   $141.39   $141.40   $141.40  
  Purchase #6 $197.68   13.448%   $224.264   $224.26   $224.25   $224.30  
  Purchase #7 $14.67   6.309%   $15.5955   $15.60   $15.60   $15.60  
  7 purchase totals = $820.58       $897.9246   $897.93   $897.95   $897.90