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 $13.68   6.736%   $14.6015   $14.60   $14.60   $14.60  
  Purchase #2 $214.76   13.863%   $244.5322   $244.53   $244.55   $244.50  
  Purchase #3 $248.70   4.671%   $260.3168   $260.32   $260.30   $260.30  
  Purchase #4 $157.27   11.578%   $175.4787   $175.48   $175.50   $175.50  
  Purchase #5 $113.74   8.678%   $123.6104   $123.61   $123.60   $123.60  
  Purchase #6 $62.26   4.582%   $65.1128   $65.11   $65.10   $65.10  
  Purchase #7 $231.26   13.511%   $262.5055   $262.51   $262.50   $262.50  
  7 purchase totals = $1,041.67       $1,146.1579   $1,146.16   $1,146.15   $1,146.10