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 $67.87   12.872%   $76.6062   $76.61   $76.60   $76.60  
  Purchase #2 $221.58   6.831%   $236.7161   $236.72   $236.70   $236.70  
  Purchase #3 $135.60   12.833%   $153.0015   $153.00   $153.00   $153.00  
  Purchase #4 $78.62   10.478%   $86.8578   $86.86   $86.85   $86.90  
  Purchase #5 $214.35   6.390%   $228.047   $228.05   $228.05   $228.00  
  Purchase #6 $139.30   8.778%   $151.5278   $151.53   $151.55   $151.50  
  Purchase #7 $7.32   12.253%   $8.2169   $8.22   $8.20   $8.20  
  7 purchase totals = $864.64       $940.9733   $940.99   $940.95   $940.90