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 $195.87   6.677%   $208.9482   $208.95   $208.95   $208.90  
  Purchase #2 $80.63   6.499%   $85.8701   $85.87   $85.85   $85.90  
  Purchase #3 $188.81   4.241%   $196.8174   $196.82   $196.80   $196.80  
  Purchase #4 $117.50   6.562%   $125.2104   $125.21   $125.20   $125.20  
  Purchase #5 $55.57   10.317%   $61.3032   $61.30   $61.30   $61.30  
  Purchase #6 $8.32   3.133%   $8.5807   $8.58   $8.60   $8.60  
  Purchase #7 $44.37   7.660%   $47.7687   $47.77   $47.75   $47.80  
  7 purchase totals = $691.07       $734.4987   $734.50   $734.45   $734.50