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 $14.82   11.177%   $16.4764   $16.48   $16.50   $16.50  
  Purchase #2 $48.53   13.385%   $55.0257   $55.03   $55.05   $55.00  
  Purchase #3 $222.26   4.116%   $231.4082   $231.41   $231.40   $231.40  
  Purchase #4 $49.34   4.262%   $51.4429   $51.44   $51.45   $51.40  
  Purchase #5 $120.94   3.602%   $125.2963   $125.30   $125.30   $125.30  
  Purchase #6 $204.94   11.224%   $227.9425   $227.94   $227.95   $227.90  
  Purchase #7 $147.45   5.637%   $155.7618   $155.76   $155.75   $155.80  
  7 purchase totals = $808.28       $863.3538   $863.36   $863.40   $863.30