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 $85.58   10.126%   $94.2458   $94.25   $94.25   $94.20  
  Purchase #2 $65.78   8.509%   $71.3772   $71.38   $71.40   $71.40  
  Purchase #3 $192.90   8.182%   $208.6831   $208.68   $208.70   $208.70  
  Purchase #4 $217.81   6.190%   $231.2924   $231.29   $231.30   $231.30  
  Purchase #5 $76.92   13.133%   $87.0219   $87.02   $87.00   $87.00  
  Purchase #6 $159.40   3.696%   $165.2914   $165.29   $165.30   $165.30  
  Purchase #7 $57.95   12.248%   $65.0477   $65.05   $65.05   $65.00  
  7 purchase totals = $856.34       $922.9595   $922.96   $923.00   $922.90