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 $140.88   8.857%   $153.3577   $153.36   $153.35   $153.40  
  Purchase #2 $175.42   12.211%   $196.8405   $196.84   $196.85   $196.80  
  Purchase #3 $113.80   9.297%   $124.38   $124.38   $124.40   $124.40  
  Purchase #4 $190.90   6.390%   $203.0985   $203.10   $203.10   $203.10  
  Purchase #5 $151.63   3.310%   $156.649   $156.65   $156.65   $156.60  
  Purchase #6 $67.55   8.549%   $73.3248   $73.32   $73.30   $73.30  
  Purchase #7 $42.59   11.680%   $47.5645   $47.56   $47.55   $47.60  
  7 purchase totals = $882.77       $955.2150   $955.21   $955.20   $955.20