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 $195.31   6.642%   $208.2825   $208.28   $208.30   $208.30  
  Purchase #2 $14.52   10.312%   $16.0173   $16.02   $16.00   $16.00  
  Purchase #3 $104.25   11.828%   $116.5807   $116.58   $116.60   $116.60  
  Purchase #4 $190.44   4.354%   $198.7318   $198.73   $198.75   $198.70  
  Purchase #5 $186.40   5.179%   $196.0537   $196.05   $196.05   $196.10  
  Purchase #6 $64.76   5.253%   $68.1618   $68.16   $68.15   $68.20  
  Purchase #7 $127.85   7.790%   $137.8095   $137.81   $137.80   $137.80  
  7 purchase totals = $883.53       $941.6373   $941.63   $941.65   $941.70