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 $58.93   9.626%   $64.6026   $64.60   $64.60   $64.60  
  Purchase #2 $44.89   8.338%   $48.6329   $48.63   $48.65   $48.60  
  Purchase #3 $168.76   13.576%   $191.6709   $191.67   $191.65   $191.70  
  Purchase #4 $111.57   7.763%   $120.2312   $120.23   $120.25   $120.20  
  Purchase #5 $196.92   8.777%   $214.2037   $214.20   $214.20   $214.20  
  Purchase #6 $187.56   4.227%   $195.4882   $195.49   $195.50   $195.50  
  Purchase #7 $164.40   12.194%   $184.4469   $184.45   $184.45   $184.40  
  7 purchase totals = $933.03       $1,019.2764   $1,019.27   $1,019.30   $1,019.20