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 $52.83   3.831%   $54.8539   $54.85   $54.85   $54.90  
  Purchase #2 $185.58   12.313%   $208.4305   $208.43   $208.45   $208.40  
  Purchase #3 $86.63   9.847%   $95.1605   $95.16   $95.15   $95.20  
  Purchase #4 $237.58   5.600%   $250.8845   $250.88   $250.90   $250.90  
  Purchase #5 $38.57   6.344%   $41.0169   $41.02   $41.00   $41.00  
  Purchase #6 $202.55   5.428%   $213.5444   $213.54   $213.55   $213.50  
  Purchase #7 $17.63   5.230%   $18.552   $18.55   $18.55   $18.60  
  7 purchase totals = $821.37       $882.4427   $882.43   $882.45   $882.50