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 $236.49   4.132%   $246.2618   $246.26   $246.25   $246.30  
  Purchase #2 $72.99   8.277%   $79.0314   $79.03   $79.05   $79.00  
  Purchase #3 $152.26   5.743%   $161.0043   $161.00   $161.00   $161.00  
  Purchase #4 $192.99   13.190%   $218.4454   $218.45   $218.45   $218.40  
  Purchase #5 $141.90   8.490%   $153.9473   $153.95   $153.95   $153.90  
  Purchase #6 $12.53   3.818%   $13.0084   $13.01   $13.00   $13.00  
  Purchase #7 $250.31   4.331%   $261.1509   $261.15   $261.15   $261.20  
  7 purchase totals = $1,059.47       $1,132.8495   $1,132.85   $1,132.85   $1,132.80