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 $206.73   9.658%   $226.696   $226.70   $226.70   $226.70  
  Purchase #2 $107.29   8.758%   $116.6865   $116.69   $116.70   $116.70  
  Purchase #3 $22.88   11.694%   $25.5556   $25.56   $25.55   $25.60  
  Purchase #4 $198.94   8.797%   $216.4408   $216.44   $216.45   $216.40  
  Purchase #5 $250.63   4.749%   $262.5324   $262.53   $262.55   $262.50  
  Purchase #6 $48.31   8.478%   $52.4057   $52.41   $52.40   $52.40  
  Purchase #7 $37.59   10.123%   $41.3952   $41.40   $41.40   $41.40  
  7 purchase totals = $872.37       $941.7122   $941.73   $941.75   $941.70