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 $217.32   13.443%   $246.5343   $246.53   $246.55   $246.50  
  Purchase #2 $166.54   9.856%   $182.9542   $182.95   $182.95   $183.00  
  Purchase #3 $59.38   13.296%   $67.2752   $67.28   $67.30   $67.30  
  Purchase #4 $123.42   6.735%   $131.7323   $131.73   $131.75   $131.70  
  Purchase #5 $190.64   4.202%   $198.6507   $198.65   $198.65   $198.70  
  Purchase #6 $118.91   13.492%   $134.9533   $134.95   $134.95   $135.00  
  Purchase #7 $236.40   7.461%   $254.0378   $254.04   $254.05   $254.00  
  7 purchase totals = $1,112.61       $1,216.1378   $1,216.13   $1,216.20   $1,216.20