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 $69.53   10.821%   $77.0538   $77.05   $77.05   $77.10  
  Purchase #2 $127.54   8.146%   $137.9294   $137.93   $137.95   $137.90  
  Purchase #3 $27.48   11.744%   $30.7073   $30.71   $30.70   $30.70  
  Purchase #4 $32.70   8.367%   $35.436   $35.44   $35.45   $35.40  
  Purchase #5 $191.34   3.873%   $198.7506   $198.75   $198.75   $198.80  
  Purchase #6 $233.53   7.252%   $250.4656   $250.47   $250.45   $250.50  
  Purchase #7 $5.44   11.720%   $6.0776   $6.08   $6.10   $6.10  
  7 purchase totals = $687.56       $736.4203   $736.43   $736.45   $736.50