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 $23.58   11.162%   $26.212   $26.21   $26.20   $26.20  
  Purchase #2 $54.93   6.685%   $58.6021   $58.60   $58.60   $58.60  
  Purchase #3 $211.62   11.744%   $236.4727   $236.47   $236.45   $236.50  
  Purchase #4 $8.27   8.720%   $8.9911   $8.99   $9.00   $9.00  
  Purchase #5 $218.55   11.624%   $243.9543   $243.95   $243.95   $244.00  
  Purchase #6 $161.91   7.135%   $173.4623   $173.46   $173.45   $173.50  
  Purchase #7 $70.91   5.834%   $75.0469   $75.05   $75.05   $75.00  
  7 purchase totals = $749.77       $822.7414   $822.73   $822.70   $822.80