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 $248.83   5.698%   $263.0083   $263.01   $263.00   $263.00  
  Purchase #2 $234.99   13.408%   $266.4975   $266.50   $266.50   $266.50  
  Purchase #3 $104.90   8.397%   $113.7085   $113.71   $113.70   $113.70  
  Purchase #4 $214.74   3.511%   $222.2795   $222.28   $222.30   $222.30  
  Purchase #5 $162.62   5.176%   $171.0372   $171.04   $171.05   $171.00  
  Purchase #6 $119.73   9.611%   $131.2373   $131.24   $131.25   $131.20  
  Purchase #7 $57.83   11.443%   $64.4475   $64.45   $64.45   $64.40  
  7 purchase totals = $1,143.64       $1,232.2158   $1,232.23   $1,232.25   $1,232.10