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 $177.47   11.866%   $198.5286   $198.53   $198.55   $198.50  
  Purchase #2 $162.94   6.471%   $173.4838   $173.48   $173.50   $173.50  
  Purchase #3 $73.84   10.533%   $81.6176   $81.62   $81.60   $81.60  
  Purchase #4 $62.36   5.541%   $65.8154   $65.82   $65.80   $65.80  
  Purchase #5 $15.56   11.118%   $17.29   $17.29   $17.30   $17.30  
  Purchase #6 $248.93   7.176%   $266.7932   $266.79   $266.80   $266.80  
  Purchase #7 $162.91   13.567%   $185.012   $185.01   $185.00   $185.00  
  7 purchase totals = $904.01       $988.5406   $988.54   $988.55   $988.50