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 $14.29   13.645%   $16.2399   $16.24   $16.25   $16.20  
  Purchase #2 $232.49   13.764%   $264.4899   $264.49   $264.50   $264.50  
  Purchase #3 $74.55   4.371%   $77.8086   $77.81   $77.80   $77.80  
  Purchase #4 $23.38   10.145%   $25.7519   $25.75   $25.75   $25.80  
  Purchase #5 $62.41   3.253%   $64.4402   $64.44   $64.45   $64.40  
  Purchase #6 $177.27   8.727%   $192.7404   $192.74   $192.75   $192.70  
  Purchase #7 $234.64   9.426%   $256.7572   $256.76   $256.75   $256.80  
  7 purchase totals = $819.03       $898.2281   $898.23   $898.25   $898.20