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 $234.97   5.673%   $248.2998   $248.30   $248.30   $248.30  
  Purchase #2 $220.38   9.836%   $242.0566   $242.06   $242.05   $242.10  
  Purchase #3 $199.61   4.378%   $208.3489   $208.35   $208.35   $208.30  
  Purchase #4 $236.42   9.779%   $259.5395   $259.54   $259.55   $259.50  
  Purchase #5 $156.88   5.722%   $165.8567   $165.86   $165.85   $165.90  
  Purchase #6 $134.42   11.184%   $149.4535   $149.45   $149.45   $149.50  
  Purchase #7 $228.47   5.794%   $241.7076   $241.71   $241.70   $241.70  
  7 purchase totals = $1,411.15       $1,515.2626   $1,515.27   $1,515.25   $1,515.30