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 $135.70   11.844%   $151.7723   $151.77   $151.75   $151.80  
  Purchase #2 $94.43   3.489%   $97.7247   $97.72   $97.70   $97.70  
  Purchase #3 $33.58   7.147%   $35.98   $35.98   $36.00   $36.00  
  Purchase #4 $59.63   10.839%   $66.0933   $66.09   $66.10   $66.10  
  Purchase #5 $18.76   5.262%   $19.7472   $19.75   $19.75   $19.70  
  Purchase #6 $209.93   8.460%   $227.6901   $227.69   $227.70   $227.70  
  Purchase #7 $101.71   9.123%   $110.989   $110.99   $111.00   $111.00  
  7 purchase totals = $653.74       $709.9966   $709.99   $710.00   $710.00