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 $52.29   11.393%   $58.2474   $58.25   $58.25   $58.20  
  Purchase #2 $30.63   10.131%   $33.7331   $33.73   $33.75   $33.70  
  Purchase #3 $58.87   5.393%   $62.0449   $62.04   $62.05   $62.00  
  Purchase #4 $96.45   5.337%   $101.5975   $101.60   $101.60   $101.60  
  Purchase #5 $222.67   3.695%   $230.8977   $230.90   $230.90   $230.90  
  Purchase #6 $192.31   11.298%   $214.0372   $214.04   $214.05   $214.00  
  Purchase #7 $175.35   12.794%   $197.7843   $197.78   $197.80   $197.80  
  7 purchase totals = $828.57       $898.3421   $898.34   $898.40   $898.20