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 $66.73   4.393%   $69.6614   $69.66   $69.65   $69.70  
  Purchase #2 $141.55   6.866%   $151.2688   $151.27   $151.25   $151.30  
  Purchase #3 $235.48   3.629%   $244.0256   $244.03   $244.05   $244.00  
  Purchase #4 $190.92   12.863%   $215.478   $215.48   $215.50   $215.50  
  Purchase #5 $175.92   12.326%   $197.6039   $197.60   $197.60   $197.60  
  Purchase #6 $198.51   9.823%   $218.0096   $218.01   $218.00   $218.00  
  Purchase #7 $126.86   8.359%   $137.4642   $137.46   $137.45   $137.50  
  7 purchase totals = $1,135.97       $1,233.5115   $1,233.51   $1,233.50   $1,233.60