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 $217.74   13.379%   $246.8714   $246.87   $246.85   $246.90  
  Purchase #2 $212.65   7.136%   $227.8247   $227.82   $227.80   $227.80  
  Purchase #3 $57.70   10.781%   $63.9206   $63.92   $63.90   $63.90  
  Purchase #4 $97.28   7.159%   $104.2443   $104.24   $104.25   $104.20  
  Purchase #5 $121.35   8.537%   $131.7096   $131.71   $131.70   $131.70  
  Purchase #6 $233.60   11.846%   $261.2723   $261.27   $261.25   $261.30  
  Purchase #7 $43.86   5.337%   $46.2008   $46.20   $46.20   $46.20  
  7 purchase totals = $984.18       $1,082.0437   $1,082.03   $1,081.95   $1,082.00