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 $241.98   10.735%   $267.9566   $267.96   $267.95   $268.00  
  Purchase #2 $150.56   7.377%   $161.6668   $161.67   $161.65   $161.70  
  Purchase #3 $175.34   6.794%   $187.2526   $187.25   $187.25   $187.30  
  Purchase #4 $30.69   5.796%   $32.4688   $32.47   $32.45   $32.50  
  Purchase #5 $232.83   8.581%   $252.8091   $252.81   $252.80   $252.80  
  Purchase #6 $73.80   3.366%   $76.2841   $76.28   $76.30   $76.30  
  Purchase #7 $15.70   7.111%   $16.8164   $16.82   $16.80   $16.80  
  7 purchase totals = $920.90       $995.2544   $995.26   $995.20   $995.40