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 $65.76   8.243%   $71.1806   $71.18   $71.20   $71.20  
  Purchase #2 $49.81   13.796%   $56.6818   $56.68   $56.70   $56.70  
  Purchase #3 $119.86   9.219%   $130.9099   $130.91   $130.90   $130.90  
  Purchase #4 $194.71   8.843%   $211.9282   $211.93   $211.95   $211.90  
  Purchase #5 $75.69   13.745%   $86.0936   $86.09   $86.10   $86.10  
  Purchase #6 $179.64   7.498%   $193.1094   $193.11   $193.10   $193.10  
  Purchase #7 $43.95   3.723%   $45.5863   $45.59   $45.60   $45.60  
  7 purchase totals = $729.42       $795.4898   $795.49   $795.55   $795.50