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 $245.28   12.723%   $276.487   $276.49   $276.50   $276.50  
  Purchase #2 $207.51   12.634%   $233.7268   $233.73   $233.75   $233.70  
  Purchase #3 $139.76   3.265%   $144.3232   $144.32   $144.30   $144.30  
  Purchase #4 $166.41   5.733%   $175.9503   $175.95   $175.95   $176.00  
  Purchase #5 $157.74   5.172%   $165.8983   $165.90   $165.90   $165.90  
  Purchase #6 $146.49   10.112%   $161.3031   $161.30   $161.30   $161.30  
  Purchase #7 $198.55   3.537%   $205.5727   $205.57   $205.55   $205.60  
  7 purchase totals = $1,261.74       $1,363.2614   $1,363.26   $1,363.25   $1,363.30