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 $33.82   3.834%   $35.1167   $35.12   $35.10   $35.10  
  Purchase #2 $53.54   13.213%   $60.6142   $60.61   $60.60   $60.60  
  Purchase #3 $94.94   12.863%   $107.1521   $107.15   $107.15   $107.20  
  Purchase #4 $213.64   13.695%   $242.898   $242.90   $242.90   $242.90  
  Purchase #5 $69.99   11.343%   $77.929   $77.93   $77.95   $77.90  
  Purchase #6 $78.74   8.456%   $85.3983   $85.40   $85.40   $85.40  
  Purchase #7 $162.68   8.829%   $177.043   $177.04   $177.05   $177.00  
  7 purchase totals = $707.35       $786.1513   $786.15   $786.15   $786.10