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 $239.74   10.840%   $265.7278   $265.73   $265.75   $265.70  
  Purchase #2 $107.51   4.719%   $112.5834   $112.58   $112.60   $112.60  
  Purchase #3 $157.53   6.187%   $167.2764   $167.28   $167.30   $167.30  
  Purchase #4 $24.93   8.566%   $27.0655   $27.07   $27.05   $27.10  
  Purchase #5 $133.66   7.833%   $144.1296   $144.13   $144.15   $144.10  
  Purchase #6 $125.90   13.514%   $142.9141   $142.91   $142.90   $142.90  
  Purchase #7 $234.74   13.514%   $266.4628   $266.46   $266.45   $266.50  
  7 purchase totals = $1,024.01       $1,126.1596   $1,126.16   $1,126.20   $1,126.20