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 $141.81   4.804%   $148.6226   $148.62   $148.60   $148.60  
  Purchase #2 $198.43   7.597%   $213.5047   $213.50   $213.50   $213.50  
  Purchase #3 $230.46   11.628%   $257.2579   $257.26   $257.25   $257.30  
  Purchase #4 $201.61   6.211%   $214.132   $214.13   $214.15   $214.10  
  Purchase #5 $144.76   8.854%   $157.5771   $157.58   $157.60   $157.60  
  Purchase #6 $207.66   3.353%   $214.6228   $214.62   $214.60   $214.60  
  Purchase #7 $152.64   9.791%   $167.585   $167.59   $167.60   $167.60  
  7 purchase totals = $1,277.37       $1,373.3021   $1,373.30   $1,373.30   $1,373.30