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 $216.56   13.602%   $246.0165   $246.02   $246.00   $246.00  
  Purchase #2 $152.61   10.866%   $169.1926   $169.19   $169.20   $169.20  
  Purchase #3 $245.36   11.730%   $274.1407   $274.14   $274.15   $274.10  
  Purchase #4 $164.42   6.866%   $175.7091   $175.71   $175.70   $175.70  
  Purchase #5 $235.82   7.685%   $253.9428   $253.94   $253.95   $253.90  
  Purchase #6 $64.28   3.469%   $66.5099   $66.51   $66.50   $66.50  
  Purchase #7 $223.99   7.109%   $239.9134   $239.91   $239.90   $239.90  
  7 purchase totals = $1,303.04       $1,425.4250   $1,425.42   $1,425.40   $1,425.30