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 $248.51   11.142%   $276.199   $276.20   $276.20   $276.20  
  Purchase #2 $12.82   12.224%   $14.3871   $14.39   $14.40   $14.40  
  Purchase #3 $82.76   6.110%   $87.8166   $87.82   $87.80   $87.80  
  Purchase #4 $63.46   4.859%   $66.5435   $66.54   $66.55   $66.50  
  Purchase #5 $114.74   7.680%   $123.552   $123.55   $123.55   $123.60  
  Purchase #6 $85.55   6.862%   $91.4204   $91.42   $91.40   $91.40  
  Purchase #7 $71.43   3.177%   $73.6993   $73.70   $73.70   $73.70  
  7 purchase totals = $679.27       $733.6179   $733.62   $733.60   $733.60