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 $98.46   5.359%   $103.7365   $103.74   $103.75   $103.70  
  Purchase #2 $25.47   10.836%   $28.2299   $28.23   $28.25   $28.20  
  Purchase #3 $163.65   11.234%   $182.0344   $182.03   $182.05   $182.00  
  Purchase #4 $241.30   10.679%   $267.0684   $267.07   $267.05   $267.10  
  Purchase #5 $183.93   8.412%   $199.4022   $199.40   $199.40   $199.40  
  Purchase #6 $62.93   3.652%   $65.2282   $65.23   $65.25   $65.20  
  Purchase #7 $159.67   11.794%   $178.5015   $178.50   $178.50   $178.50  
  7 purchase totals = $935.41       $1,024.2011   $1,024.20   $1,024.25   $1,024.10