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 $76.41   7.246%   $81.9467   $81.95   $81.95   $81.90  
  Purchase #2 $211.37   13.293%   $239.4674   $239.47   $239.45   $239.50  
  Purchase #3 $214.43   7.665%   $230.8661   $230.87   $230.85   $230.90  
  Purchase #4 $75.74   5.471%   $79.8837   $79.88   $79.90   $79.90  
  Purchase #5 $248.48   4.672%   $260.089   $260.09   $260.10   $260.10  
  Purchase #6 $138.92   11.699%   $155.1723   $155.17   $155.15   $155.20  
  Purchase #7 $54.59   3.835%   $56.6835   $56.68   $56.70   $56.70  
  7 purchase totals = $1,019.94       $1,104.1087   $1,104.11   $1,104.10   $1,104.20