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 $233.54   12.505%   $262.7442   $262.74   $262.75   $262.70  
  Purchase #2 $151.83   7.167%   $162.7117   $162.71   $162.70   $162.70  
  Purchase #3 $236.34   8.189%   $255.6939   $255.69   $255.70   $255.70  
  Purchase #4 $234.54   3.535%   $242.831   $242.83   $242.85   $242.80  
  Purchase #5 $129.81   4.123%   $135.1621   $135.16   $135.15   $135.20  
  Purchase #6 $240.72   9.142%   $262.7266   $262.73   $262.75   $262.70  
  Purchase #7 $195.90   9.838%   $215.1726   $215.17   $215.15   $215.20  
  7 purchase totals = $1,422.68       $1,537.0421   $1,537.03   $1,537.05   $1,537.00