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 $30.89   7.674%   $33.2605   $33.26   $33.25   $33.30  
  Purchase #2 $126.62   12.663%   $142.6539   $142.65   $142.65   $142.70  
  Purchase #3 $221.93   10.838%   $245.9828   $245.98   $246.00   $246.00  
  Purchase #4 $219.45   11.847%   $245.4482   $245.45   $245.45   $245.40  
  Purchase #5 $250.67   4.482%   $261.905   $261.91   $261.90   $261.90  
  Purchase #6 $199.91   13.770%   $227.4376   $227.44   $227.45   $227.40  
  Purchase #7 $167.28   8.146%   $180.9066   $180.91   $180.90   $180.90  
  7 purchase totals = $1,216.75       $1,337.5946   $1,337.60   $1,337.60   $1,337.60