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 $171.91   8.727%   $186.9126   $186.91   $186.90   $186.90  
  Purchase #2 $58.61   4.271%   $61.1132   $61.11   $61.10   $61.10  
  Purchase #3 $16.48   7.609%   $17.734   $17.73   $17.75   $17.70  
  Purchase #4 $233.39   7.481%   $250.8499   $250.85   $250.85   $250.80  
  Purchase #5 $58.41   7.685%   $62.8988   $62.90   $62.90   $62.90  
  Purchase #6 $214.46   10.135%   $236.1955   $236.20   $236.20   $236.20  
  Purchase #7 $124.34   7.255%   $133.3609   $133.36   $133.35   $133.40  
  7 purchase totals = $877.60       $949.0649   $949.06   $949.05   $949.00