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 $63.63   5.587%   $67.185   $67.19   $67.20   $67.20  
  Purchase #2 $39.49   12.577%   $44.4567   $44.46   $44.45   $44.50  
  Purchase #3 $118.35   12.338%   $132.952   $132.95   $132.95   $133.00  
  Purchase #4 $85.76   10.320%   $94.6104   $94.61   $94.60   $94.60  
  Purchase #5 $89.35   5.405%   $94.1794   $94.18   $94.20   $94.20  
  Purchase #6 $229.37   3.539%   $237.4874   $237.49   $237.50   $237.50  
  Purchase #7 $246.66   9.141%   $269.2072   $269.21   $269.20   $269.20  
  7 purchase totals = $872.61       $940.0781   $940.09   $940.10   $940.20