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 $153.90   4.727%   $161.1749   $161.17   $161.15   $161.20  
  Purchase #2 $112.39   9.357%   $122.9063   $122.91   $122.90   $122.90  
  Purchase #3 $188.46   13.345%   $213.61   $213.61   $213.60   $213.60  
  Purchase #4 $46.83   10.454%   $51.7256   $51.73   $51.75   $51.70  
  Purchase #5 $194.63   8.473%   $211.121   $211.12   $211.10   $211.10  
  Purchase #6 $63.45   13.295%   $71.8857   $71.89   $71.90   $71.90  
  Purchase #7 $124.93   5.401%   $131.6775   $131.68   $131.70   $131.70  
  7 purchase totals = $884.59       $964.1010   $964.11   $964.10   $964.10