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 $56.81   8.242%   $61.4923   $61.49   $61.50   $61.50  
  Purchase #2 $66.39   7.116%   $71.1143   $71.11   $71.10   $71.10  
  Purchase #3 $166.78   10.191%   $183.7765   $183.78   $183.80   $183.80  
  Purchase #4 $58.46   4.406%   $61.0357   $61.04   $61.05   $61.00  
  Purchase #5 $64.63   3.722%   $67.0355   $67.04   $67.05   $67.00  
  Purchase #6 $26.93   13.819%   $30.6515   $30.65   $30.65   $30.70  
  Purchase #7 $12.99   12.764%   $14.648   $14.65   $14.65   $14.60  
  7 purchase totals = $452.99       $489.7538   $489.76   $489.80   $489.70