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 $156.94   7.605%   $168.8753   $168.88   $168.90   $168.90  
  Purchase #2 $240.91   10.810%   $266.9524   $266.95   $266.95   $267.00  
  Purchase #3 $44.43   13.160%   $50.277   $50.28   $50.30   $50.30  
  Purchase #4 $153.30   5.674%   $161.9982   $162.00   $162.00   $162.00  
  Purchase #5 $35.31   6.741%   $37.6902   $37.69   $37.70   $37.70  
  Purchase #6 $118.96   4.442%   $124.2442   $124.24   $124.25   $124.20  
  Purchase #7 $8.46   6.376%   $8.9994   $9.00   $9.00   $9.00  
  7 purchase totals = $758.31       $819.0367   $819.04   $819.10   $819.10