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 $55.53   9.575%   $60.847   $60.85   $60.85   $60.80  
  Purchase #2 $118.58   6.346%   $126.1051   $126.11   $126.10   $126.10  
  Purchase #3 $27.95   5.436%   $29.4694   $29.47   $29.45   $29.50  
  Purchase #4 $13.62   13.407%   $15.446   $15.45   $15.45   $15.40  
  Purchase #5 $232.38   12.758%   $262.027   $262.03   $262.05   $262.00  
  Purchase #6 $166.77   12.814%   $188.1399   $188.14   $188.15   $188.10  
  Purchase #7 $92.56   13.128%   $104.7113   $104.71   $104.70   $104.70  
  7 purchase totals = $707.39       $786.7457   $786.76   $786.75   $786.60