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 $198.63   13.784%   $226.0092   $226.01   $226.00   $226.00  
  Purchase #2 $21.28   11.104%   $23.6429   $23.64   $23.65   $23.60  
  Purchase #3 $208.90   4.188%   $217.6487   $217.65   $217.65   $217.60  
  Purchase #4 $93.47   8.361%   $101.285   $101.29   $101.30   $101.30  
  Purchase #5 $226.25   7.175%   $242.4834   $242.48   $242.50   $242.50  
  Purchase #6 $65.33   13.121%   $73.9019   $73.90   $73.90   $73.90  
  Purchase #7 $240.86   12.728%   $271.5167   $271.52   $271.50   $271.50  
  7 purchase totals = $1,054.72       $1,156.4878   $1,156.49   $1,156.50   $1,156.40