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 $201.27   10.111%   $221.6204   $221.62   $221.60   $221.60  
  Purchase #2 $131.34   9.672%   $144.0432   $144.04   $144.05   $144.00  
  Purchase #3 $15.53   8.228%   $16.8078   $16.81   $16.80   $16.80  
  Purchase #4 $22.81   9.568%   $24.9925   $24.99   $25.00   $25.00  
  Purchase #5 $166.36   11.473%   $185.4465   $185.45   $185.45   $185.40  
  Purchase #6 $88.55   11.602%   $98.8236   $98.82   $98.80   $98.80  
  Purchase #7 $30.93   6.821%   $33.0397   $33.04   $33.05   $33.00  
  7 purchase totals = $656.79       $724.7737   $724.77   $724.75   $724.60