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 $71.81   4.660%   $75.1563   $75.16   $75.15   $75.20  
  Purchase #2 $227.59   3.825%   $236.2953   $236.30   $236.30   $236.30  
  Purchase #3 $159.60   3.706%   $165.5148   $165.51   $165.50   $165.50  
  Purchase #4 $58.76   8.215%   $63.5871   $63.59   $63.60   $63.60  
  Purchase #5 $119.47   5.300%   $125.8019   $125.80   $125.80   $125.80  
  Purchase #6 $74.95   9.181%   $81.8312   $81.83   $81.85   $81.80  
  Purchase #7 $66.61   4.527%   $69.6254   $69.63   $69.65   $69.60  
  7 purchase totals = $778.79       $817.8120   $817.82   $817.85   $817.80