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 $57.36   9.871%   $63.022   $63.02   $63.00   $63.00  
  Purchase #2 $83.69   12.493%   $94.1454   $94.15   $94.15   $94.10  
  Purchase #3 $156.45   12.711%   $176.3364   $176.34   $176.35   $176.30  
  Purchase #4 $153.90   3.242%   $158.8894   $158.89   $158.90   $158.90  
  Purchase #5 $181.74   7.703%   $195.7394   $195.74   $195.75   $195.70  
  Purchase #6 $186.27   13.201%   $210.8595   $210.86   $210.85   $210.90  
  Purchase #7 $22.83   4.438%   $23.8432   $23.84   $23.85   $23.80  
  7 purchase totals = $842.24       $922.8353   $922.84   $922.85   $922.70