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 $199.61   4.616%   $208.824   $208.82   $208.80   $208.80  
  Purchase #2 $183.69   8.321%   $198.9748   $198.97   $198.95   $199.00  
  Purchase #3 $53.49   13.489%   $60.7053   $60.71   $60.70   $60.70  
  Purchase #4 $161.47   5.651%   $170.5947   $170.59   $170.60   $170.60  
  Purchase #5 $83.64   12.666%   $94.2338   $94.23   $94.25   $94.20  
  Purchase #6 $97.63   7.552%   $105.003   $105.00   $105.00   $105.00  
  Purchase #7 $124.85   4.643%   $130.6468   $130.65   $130.65   $130.60  
  7 purchase totals = $904.38       $968.9824   $968.97   $968.95   $968.90