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 $34.72   8.377%   $37.6285   $37.63   $37.65   $37.60  
  Purchase #2 $96.27   12.814%   $108.606   $108.61   $108.60   $108.60  
  Purchase #3 $7.26   13.665%   $8.2521   $8.25   $8.25   $8.30  
  Purchase #4 $206.75   4.713%   $216.4941   $216.49   $216.50   $216.50  
  Purchase #5 $236.44   13.748%   $268.9458   $268.95   $268.95   $268.90  
  Purchase #6 $86.85   13.793%   $98.8292   $98.83   $98.85   $98.80  
  Purchase #7 $96.81   11.732%   $108.1677   $108.17   $108.15   $108.20  
  7 purchase totals = $765.10       $846.9234   $846.93   $846.95   $846.90