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 $157.68   9.726%   $173.016   $173.02   $173.00   $173.00  
  Purchase #2 $25.51   10.125%   $28.0929   $28.09   $28.10   $28.10  
  Purchase #3 $179.98   9.435%   $196.9611   $196.96   $196.95   $197.00  
  Purchase #4 $137.94   11.549%   $153.8707   $153.87   $153.85   $153.90  
  Purchase #5 $83.46   7.246%   $89.5075   $89.51   $89.50   $89.50  
  Purchase #6 $73.88   3.440%   $76.4215   $76.42   $76.40   $76.40  
  Purchase #7 $17.76   5.595%   $18.7537   $18.75   $18.75   $18.80  
  7 purchase totals = $676.21       $736.6234   $736.62   $736.55   $736.70