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 $33.33   11.725%   $37.2379   $37.24   $37.25   $37.20  
  Purchase #2 $143.63   9.146%   $156.7664   $156.77   $156.75   $156.80  
  Purchase #3 $150.41   4.769%   $157.5831   $157.58   $157.60   $157.60  
  Purchase #4 $147.25   4.706%   $154.1796   $154.18   $154.20   $154.20  
  Purchase #5 $191.72   3.872%   $199.1434   $199.14   $199.15   $199.10  
  Purchase #6 $20.69   12.405%   $23.2566   $23.26   $23.25   $23.30  
  Purchase #7 $239.54   11.439%   $266.941   $266.94   $266.95   $266.90  
  7 purchase totals = $926.57       $995.1080   $995.11   $995.15   $995.10