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 $192.36   8.124%   $207.9873   $207.99   $208.00   $208.00  
  Purchase #2 $53.89   3.354%   $55.6975   $55.70   $55.70   $55.70  
  Purchase #3 $65.56   13.192%   $74.2087   $74.21   $74.20   $74.20  
  Purchase #4 $181.37   11.462%   $202.1586   $202.16   $202.15   $202.20  
  Purchase #5 $216.65   9.262%   $236.7161   $236.72   $236.70   $236.70  
  Purchase #6 $132.42   7.173%   $141.9185   $141.92   $141.90   $141.90  
  Purchase #7 $45.91   3.466%   $47.5012   $47.50   $47.50   $47.50  
  7 purchase totals = $888.16       $966.1879   $966.20   $966.15   $966.20