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 $62.63   6.375%   $66.6227   $66.62   $66.60   $66.60  
  Purchase #2 $111.25   10.477%   $122.9057   $122.91   $122.90   $122.90  
  Purchase #3 $18.44   5.402%   $19.4361   $19.44   $19.45   $19.40  
  Purchase #4 $215.60   6.749%   $230.1508   $230.15   $230.15   $230.20  
  Purchase #5 $21.35   12.145%   $23.943   $23.94   $23.95   $23.90  
  Purchase #6 $198.34   9.510%   $217.2021   $217.20   $217.20   $217.20  
  Purchase #7 $216.69   11.771%   $242.1966   $242.20   $242.20   $242.20  
  7 purchase totals = $844.30       $922.4570   $922.46   $922.45   $922.40