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 $96.41   10.242%   $106.2843   $106.28   $106.30   $106.30  
  Purchase #2 $68.48   10.350%   $75.5677   $75.57   $75.55   $75.60  
  Purchase #3 $92.68   11.366%   $103.214   $103.21   $103.20   $103.20  
  Purchase #4 $23.78   11.301%   $26.4674   $26.47   $26.45   $26.50  
  Purchase #5 $177.56   4.391%   $185.3567   $185.36   $185.35   $185.40  
  Purchase #6 $180.72   6.548%   $192.5535   $192.55   $192.55   $192.60  
  Purchase #7 $23.92   12.470%   $26.9028   $26.90   $26.90   $26.90  
  7 purchase totals = $663.55       $716.3464   $716.34   $716.30   $716.50