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 $110.68   8.172%   $119.7248   $119.72   $119.70   $119.70  
  Purchase #2 $13.96   7.641%   $15.0267   $15.03   $15.05   $15.00  
  Purchase #3 $237.81   3.118%   $245.2249   $245.22   $245.20   $245.20  
  Purchase #4 $58.33   6.177%   $61.933   $61.93   $61.95   $61.90  
  Purchase #5 $137.96   10.324%   $152.203   $152.20   $152.20   $152.20  
  Purchase #6 $176.82   5.212%   $186.0359   $186.04   $186.05   $186.00  
  Purchase #7 $109.42   7.793%   $117.9471   $117.95   $117.95   $117.90  
  7 purchase totals = $844.98       $898.0954   $898.09   $898.10   $897.90