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 $60.91   3.410%   $62.987   $62.99   $63.00   $63.00  
  Purchase #2 $58.32   12.536%   $65.631   $65.63   $65.65   $65.60  
  Purchase #3 $34.29   12.266%   $38.496   $38.50   $38.50   $38.50  
  Purchase #4 $23.61   11.159%   $26.2446   $26.24   $26.25   $26.20  
  Purchase #5 $217.93   11.203%   $242.3447   $242.34   $242.35   $242.30  
  Purchase #6 $91.31   11.624%   $101.9239   $101.92   $101.90   $101.90  
  Purchase #7 $25.57   4.117%   $26.6227   $26.62   $26.60   $26.60  
  7 purchase totals = $511.94       $564.2499   $564.24   $564.25   $564.10