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 $201.37   3.716%   $208.8529   $208.85   $208.85   $208.90  
  Purchase #2 $84.69   11.433%   $94.3726   $94.37   $94.35   $94.40  
  Purchase #3 $111.59   12.752%   $125.82   $125.82   $125.80   $125.80  
  Purchase #4 $164.62   13.343%   $186.5852   $186.59   $186.60   $186.60  
  Purchase #5 $34.80   6.162%   $36.9444   $36.94   $36.95   $36.90  
  Purchase #6 $118.86   11.635%   $132.6894   $132.69   $132.70   $132.70  
  Purchase #7 $171.99   7.278%   $184.5074   $184.51   $184.50   $184.50  
  7 purchase totals = $887.92       $969.7719   $969.77   $969.75   $969.80