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 $174.89   12.842%   $197.3494   $197.35   $197.35   $197.30  
  Purchase #2 $214.27   11.268%   $238.4139   $238.41   $238.40   $238.40  
  Purchase #3 $248.44   5.272%   $261.5378   $261.54   $261.55   $261.50  
  Purchase #4 $166.69   11.454%   $185.7827   $185.78   $185.80   $185.80  
  Purchase #5 $198.78   4.272%   $207.2719   $207.27   $207.25   $207.30  
  Purchase #6 $107.46   6.249%   $114.1752   $114.18   $114.20   $114.20  
  Purchase #7 $157.64   5.822%   $166.8178   $166.82   $166.80   $166.80  
  7 purchase totals = $1,268.17       $1,371.3487   $1,371.35   $1,371.35   $1,371.30