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 $246.94   10.594%   $273.1008   $273.10   $273.10   $273.10  
  Purchase #2 $18.84   10.634%   $20.8434   $20.84   $20.85   $20.80  
  Purchase #3 $15.73   5.110%   $16.5338   $16.53   $16.55   $16.50  
  Purchase #4 $95.47   8.838%   $103.9076   $103.91   $103.90   $103.90  
  Purchase #5 $59.44   12.172%   $66.675   $66.68   $66.70   $66.70  
  Purchase #6 $75.76   9.140%   $82.6845   $82.68   $82.70   $82.70  
  Purchase #7 $151.59   8.453%   $164.4039   $164.40   $164.40   $164.40  
  7 purchase totals = $663.77       $728.1490   $728.14   $728.20   $728.10