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 $74.83   9.698%   $82.087   $82.09   $82.10   $82.10  
  Purchase #2 $24.47   3.260%   $25.2677   $25.27   $25.25   $25.30  
  Purchase #3 $26.69   3.766%   $27.6951   $27.70   $27.70   $27.70  
  Purchase #4 $178.77   6.795%   $190.9174   $190.92   $190.90   $190.90  
  Purchase #5 $7.84   4.463%   $8.1899   $8.19   $8.20   $8.20  
  Purchase #6 $93.87   7.759%   $101.1534   $101.15   $101.15   $101.20  
  Purchase #7 $207.57   3.588%   $215.0176   $215.02   $215.00   $215.00  
  7 purchase totals = $614.04       $650.3281   $650.34   $650.30   $650.40