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 $226.53   4.551%   $236.8394   $236.84   $236.85   $236.80  
  Purchase #2 $144.49   11.859%   $161.6251   $161.63   $161.65   $161.60  
  Purchase #3 $91.93   4.333%   $95.9133   $95.91   $95.90   $95.90  
  Purchase #4 $222.41   11.271%   $247.4778   $247.48   $247.50   $247.50  
  Purchase #5 $172.28   11.847%   $192.69   $192.69   $192.70   $192.70  
  Purchase #6 $241.48   6.613%   $257.4491   $257.45   $257.45   $257.40  
  Purchase #7 $225.89   10.758%   $250.1912   $250.19   $250.20   $250.20  
  7 purchase totals = $1,325.01       $1,442.1859   $1,442.19   $1,442.25   $1,442.10