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 $246.75   13.152%   $279.2026   $279.20   $279.20   $279.20  
  Purchase #2 $209.46   8.757%   $227.8024   $227.80   $227.80   $227.80  
  Purchase #3 $66.71   3.400%   $68.9781   $68.98   $69.00   $69.00  
  Purchase #4 $182.77   11.467%   $203.7282   $203.73   $203.75   $203.70  
  Purchase #5 $234.43   13.584%   $266.275   $266.28   $266.30   $266.30  
  Purchase #6 $248.29   6.742%   $265.0297   $265.03   $265.05   $265.00  
  Purchase #7 $207.26   6.712%   $221.1713   $221.17   $221.15   $221.20  
  7 purchase totals = $1,395.67       $1,532.1873   $1,532.19   $1,532.25   $1,532.20