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 $239.83   11.523%   $267.4656   $267.47   $267.45   $267.50  
  Purchase #2 $250.71   11.626%   $279.8575   $279.86   $279.85   $279.90  
  Purchase #3 $134.31   8.811%   $146.1441   $146.14   $146.15   $146.10  
  Purchase #4 $190.72   9.291%   $208.4398   $208.44   $208.45   $208.40  
  Purchase #5 $225.80   7.325%   $242.3399   $242.34   $242.35   $242.30  
  Purchase #6 $115.38   11.247%   $128.3568   $128.36   $128.35   $128.40  
  Purchase #7 $190.30   6.308%   $202.3041   $202.30   $202.30   $202.30  
  7 purchase totals = $1,347.05       $1,474.9078   $1,474.91   $1,474.90   $1,474.90