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 $242.67   10.526%   $268.2134   $268.21   $268.20   $268.20  
  Purchase #2 $208.67   4.165%   $217.3611   $217.36   $217.35   $217.40  
  Purchase #3 $211.51   3.295%   $218.4793   $218.48   $218.50   $218.50  
  Purchase #4 $227.71   4.517%   $237.9957   $238.00   $238.00   $238.00  
  Purchase #5 $101.77   6.526%   $108.4115   $108.41   $108.40   $108.40  
  Purchase #6 $246.63   9.561%   $270.2103   $270.21   $270.20   $270.20  
  Purchase #7 $5.73   3.607%   $5.9367   $5.94   $5.95   $5.90  
  7 purchase totals = $1,244.69       $1,326.6080   $1,326.61   $1,326.60   $1,326.60