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 $216.95   7.143%   $232.4467   $232.45   $232.45   $232.40  
  Purchase #2 $249.72   3.249%   $257.8334   $257.83   $257.85   $257.80  
  Purchase #3 $63.38   10.357%   $69.9443   $69.94   $69.95   $69.90  
  Purchase #4 $236.58   9.568%   $259.216   $259.22   $259.20   $259.20  
  Purchase #5 $21.28   9.639%   $23.3312   $23.33   $23.35   $23.30  
  Purchase #6 $96.80   8.688%   $105.21   $105.21   $105.20   $105.20  
  Purchase #7 $5.56   12.750%   $6.2689   $6.27   $6.25   $6.30  
  7 purchase totals = $890.27       $954.2505   $954.25   $954.25   $954.10