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 $105.89   12.648%   $119.283   $119.28   $119.30   $119.30  
  Purchase #2 $69.65   7.400%   $74.8041   $74.80   $74.80   $74.80  
  Purchase #3 $91.49   12.385%   $102.821   $102.82   $102.80   $102.80  
  Purchase #4 $32.84   8.858%   $35.749   $35.75   $35.75   $35.70  
  Purchase #5 $164.73   5.194%   $173.2861   $173.29   $173.30   $173.30  
  Purchase #6 $141.67   12.202%   $158.9566   $158.96   $158.95   $159.00  
  Purchase #7 $125.51   13.520%   $142.479   $142.48   $142.50   $142.50  
  7 purchase totals = $731.78       $807.3788   $807.38   $807.40   $807.40