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 $92.67   12.544%   $104.2945   $104.29   $104.30   $104.30  
  Purchase #2 $68.81   4.865%   $72.1576   $72.16   $72.15   $72.20  
  Purchase #3 $215.68   10.145%   $237.5607   $237.56   $237.55   $237.60  
  Purchase #4 $71.27   9.292%   $77.8924   $77.89   $77.90   $77.90  
  Purchase #5 $50.65   13.783%   $57.6311   $57.63   $57.65   $57.60  
  Purchase #6 $27.49   3.806%   $28.5363   $28.54   $28.55   $28.50  
  Purchase #7 $45.79   8.597%   $49.7266   $49.73   $49.75   $49.70  
  7 purchase totals = $572.36       $627.7992   $627.80   $627.85   $627.80