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 $224.36   13.290%   $254.1774   $254.18   $254.20   $254.20  
  Purchase #2 $75.26   13.775%   $85.6271   $85.63   $85.65   $85.60  
  Purchase #3 $226.40   11.340%   $252.0738   $252.07   $252.05   $252.10  
  Purchase #4 $226.83   10.604%   $250.8831   $250.88   $250.90   $250.90  
  Purchase #5 $230.71   5.158%   $242.61   $242.61   $242.60   $242.60  
  Purchase #6 $193.65   6.593%   $206.4173   $206.42   $206.40   $206.40  
  Purchase #7 $244.55   7.527%   $262.9573   $262.96   $262.95   $263.00  
  7 purchase totals = $1,421.76       $1,554.7460   $1,554.75   $1,554.75   $1,554.80