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 $136.82   6.873%   $146.2236   $146.22   $146.20   $146.20  
  Purchase #2 $55.29   4.198%   $57.6111   $57.61   $57.60   $57.60  
  Purchase #3 $242.58   11.468%   $270.3991   $270.40   $270.40   $270.40  
  Purchase #4 $109.76   6.465%   $116.856   $116.86   $116.85   $116.90  
  Purchase #5 $47.26   6.175%   $50.1783   $50.18   $50.20   $50.20  
  Purchase #6 $206.40   9.406%   $225.814   $225.81   $225.80   $225.80  
  Purchase #7 $112.37   4.367%   $117.2772   $117.28   $117.30   $117.30  
  7 purchase totals = $910.48       $984.3593   $984.36   $984.35   $984.40