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 $95.59   9.192%   $104.3766   $104.38   $104.40   $104.40  
  Purchase #2 $110.63   8.402%   $119.9251   $119.93   $119.95   $119.90  
  Purchase #3 $47.69   4.235%   $49.7097   $49.71   $49.70   $49.70  
  Purchase #4 $164.84   13.823%   $187.6258   $187.63   $187.65   $187.60  
  Purchase #5 $69.57   6.505%   $74.0955   $74.10   $74.10   $74.10  
  Purchase #6 $212.50   9.303%   $232.2689   $232.27   $232.25   $232.30  
  Purchase #7 $51.27   5.853%   $54.2708   $54.27   $54.25   $54.30  
  7 purchase totals = $752.09       $822.2724   $822.29   $822.30   $822.30