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 $201.61   7.597%   $216.9263   $216.93   $216.95   $216.90  
  Purchase #2 $158.68   10.865%   $175.9206   $175.92   $175.90   $175.90  
  Purchase #3 $134.63   8.455%   $146.013   $146.01   $146.00   $146.00  
  Purchase #4 $170.48   5.139%   $179.241   $179.24   $179.25   $179.20  
  Purchase #5 $175.30   3.110%   $180.7518   $180.75   $180.75   $180.80  
  Purchase #6 $112.95   5.554%   $119.2232   $119.22   $119.20   $119.20  
  Purchase #7 $5.58   13.723%   $6.3457   $6.35   $6.35   $6.30  
  7 purchase totals = $959.23       $1,024.4216   $1,024.42   $1,024.40   $1,024.30