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 $191.39   8.491%   $207.6409   $207.64   $207.65   $207.60  
  Purchase #2 $236.27   11.793%   $264.1333   $264.13   $264.15   $264.10  
  Purchase #3 $14.50   12.151%   $16.2619   $16.26   $16.25   $16.30  
  Purchase #4 $93.63   4.859%   $98.1795   $98.18   $98.20   $98.20  
  Purchase #5 $186.57   10.516%   $206.1897   $206.19   $206.20   $206.20  
  Purchase #6 $216.30   5.330%   $227.8288   $227.83   $227.85   $227.80  
  Purchase #7 $207.43   13.809%   $236.074   $236.07   $236.05   $236.10  
  7 purchase totals = $1,146.09       $1,256.3081   $1,256.30   $1,256.35   $1,256.30