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 $234.75   9.195%   $256.3353   $256.34   $256.35   $256.30  
  Purchase #2 $20.78   8.858%   $22.6207   $22.62   $22.60   $22.60  
  Purchase #3 $12.81   5.288%   $13.4874   $13.49   $13.50   $13.50  
  Purchase #4 $81.93   9.388%   $89.6216   $89.62   $89.60   $89.60  
  Purchase #5 $109.64   4.574%   $114.6549   $114.65   $114.65   $114.70  
  Purchase #6 $13.46   13.694%   $15.3032   $15.30   $15.30   $15.30  
  Purchase #7 $229.84   9.130%   $250.8244   $250.82   $250.80   $250.80  
  7 purchase totals = $703.21       $762.8475   $762.84   $762.80   $762.80