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 $239.60   4.655%   $250.7534   $250.75   $250.75   $250.80  
  Purchase #2 $171.47   13.788%   $195.1123   $195.11   $195.10   $195.10  
  Purchase #3 $105.38   11.401%   $117.3944   $117.39   $117.40   $117.40  
  Purchase #4 $50.46   6.176%   $53.5764   $53.58   $53.60   $53.60  
  Purchase #5 $64.50   12.279%   $72.42   $72.42   $72.40   $72.40  
  Purchase #6 $69.47   8.693%   $75.509   $75.51   $75.50   $75.50  
  Purchase #7 $114.69   5.214%   $120.6699   $120.67   $120.65   $120.70  
  7 purchase totals = $815.57       $885.4354   $885.43   $885.40   $885.50