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 $141.33   9.109%   $154.2037   $154.20   $154.20   $154.20  
  Purchase #2 $94.63   13.466%   $107.3729   $107.37   $107.35   $107.40  
  Purchase #3 $86.69   13.315%   $98.2328   $98.23   $98.25   $98.20  
  Purchase #4 $197.59   8.268%   $213.9267   $213.93   $213.95   $213.90  
  Purchase #5 $210.64   12.398%   $236.7551   $236.76   $236.75   $236.80  
  Purchase #6 $59.50   11.461%   $66.3193   $66.32   $66.30   $66.30  
  Purchase #7 $26.83   10.582%   $29.6692   $29.67   $29.65   $29.70  
  7 purchase totals = $817.21       $906.4797   $906.48   $906.45   $906.50