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 $203.76   9.532%   $223.1824   $223.18   $223.20   $223.20  
  Purchase #2 $109.67   5.656%   $115.8729   $115.87   $115.85   $115.90  
  Purchase #3 $84.79   8.770%   $92.2261   $92.23   $92.25   $92.20  
  Purchase #4 $241.74   7.533%   $259.9503   $259.95   $259.95   $260.00  
  Purchase #5 $5.95   10.462%   $6.5725   $6.57   $6.55   $6.60  
  Purchase #6 $175.99   5.861%   $186.3048   $186.30   $186.30   $186.30  
  Purchase #7 $74.30   5.276%   $78.2201   $78.22   $78.20   $78.20  
  7 purchase totals = $896.20       $962.3291   $962.32   $962.30   $962.40