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 $59.49   7.861%   $64.1665   $64.17   $64.15   $64.20  
  Purchase #2 $245.43   8.429%   $266.1173   $266.12   $266.10   $266.10  
  Purchase #3 $113.69   5.646%   $120.1089   $120.11   $120.10   $120.10  
  Purchase #4 $75.80   3.541%   $78.4841   $78.48   $78.50   $78.50  
  Purchase #5 $194.49   3.158%   $200.632   $200.63   $200.65   $200.60  
  Purchase #6 $81.91   5.387%   $86.3225   $86.32   $86.30   $86.30  
  Purchase #7 $123.27   13.647%   $140.0927   $140.09   $140.10   $140.10  
  7 purchase totals = $894.08       $955.9240   $955.92   $955.90   $955.90