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 $233.93   9.540%   $256.2469   $256.25   $256.25   $256.20  
  Purchase #2 $181.89   13.470%   $206.3906   $206.39   $206.40   $206.40  
  Purchase #3 $53.61   3.309%   $55.384   $55.38   $55.40   $55.40  
  Purchase #4 $68.53   7.623%   $73.754   $73.75   $73.75   $73.80  
  Purchase #5 $114.84   8.107%   $124.1501   $124.15   $124.15   $124.20  
  Purchase #6 $143.60   9.573%   $157.3468   $157.35   $157.35   $157.30  
  Purchase #7 $69.71   9.644%   $76.4328   $76.43   $76.45   $76.40  
  7 purchase totals = $866.11       $949.7052   $949.70   $949.75   $949.70