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 $216.96   3.262%   $224.0372   $224.04   $224.05   $224.00  
  Purchase #2 $172.38   11.255%   $191.7814   $191.78   $191.80   $191.80  
  Purchase #3 $221.25   12.604%   $249.1364   $249.14   $249.15   $249.10  
  Purchase #4 $9.38   3.276%   $9.6873   $9.69   $9.70   $9.70  
  Purchase #5 $70.34   7.449%   $75.5796   $75.58   $75.60   $75.60  
  Purchase #6 $182.87   13.756%   $208.0256   $208.03   $208.05   $208.00  
  Purchase #7 $32.94   11.234%   $36.6405   $36.64   $36.65   $36.60  
  7 purchase totals = $906.12       $994.8880   $994.90   $995.00   $994.80