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 $56.64   10.744%   $62.7254   $62.73   $62.75   $62.70  
  Purchase #2 $118.71   10.207%   $130.8267   $130.83   $130.85   $130.80  
  Purchase #3 $90.39   9.239%   $98.7411   $98.74   $98.75   $98.70  
  Purchase #4 $176.69   11.780%   $197.5041   $197.50   $197.50   $197.50  
  Purchase #5 $70.77   5.558%   $74.7034   $74.70   $74.70   $74.70  
  Purchase #6 $141.99   13.599%   $161.2992   $161.30   $161.30   $161.30  
  Purchase #7 $51.55   3.679%   $53.4465   $53.45   $53.45   $53.40  
  7 purchase totals = $706.74       $779.2464   $779.25   $779.30   $779.10