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 $151.84   13.738%   $172.6998   $172.70   $172.70   $172.70  
  Purchase #2 $51.51   10.525%   $56.9314   $56.93   $56.95   $56.90  
  Purchase #3 $81.36   5.830%   $86.1033   $86.10   $86.10   $86.10  
  Purchase #4 $89.39   6.548%   $95.2433   $95.24   $95.25   $95.20  
  Purchase #5 $241.73   12.719%   $272.4756   $272.48   $272.50   $272.50  
  Purchase #6 $116.61   6.334%   $123.9961   $124.00   $124.00   $124.00  
  Purchase #7 $122.80   3.458%   $127.0464   $127.05   $127.05   $127.00  
  7 purchase totals = $855.24       $934.4959   $934.50   $934.55   $934.40