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 $48.51   3.130%   $50.0284   $50.03   $50.05   $50.00  
  Purchase #2 $96.54   12.611%   $108.7147   $108.71   $108.70   $108.70  
  Purchase #3 $244.96   11.394%   $272.8707   $272.87   $272.85   $272.90  
  Purchase #4 $216.67   9.217%   $236.6405   $236.64   $236.65   $236.60  
  Purchase #5 $233.58   10.395%   $257.8606   $257.86   $257.85   $257.90  
  Purchase #6 $86.57   13.384%   $98.1565   $98.16   $98.15   $98.20  
  Purchase #7 $244.99   8.429%   $265.6402   $265.64   $265.65   $265.60  
  7 purchase totals = $1,171.82       $1,289.9116   $1,289.91   $1,289.90   $1,289.90