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 $197.72   5.327%   $208.2525   $208.25   $208.25   $208.30  
  Purchase #2 $53.73   13.175%   $60.8089   $60.81   $60.80   $60.80  
  Purchase #3 $104.73   8.730%   $113.8729   $113.87   $113.85   $113.90  
  Purchase #4 $92.43   4.189%   $96.3019   $96.30   $96.30   $96.30  
  Purchase #5 $75.44   5.786%   $79.805   $79.81   $79.80   $79.80  
  Purchase #6 $199.56   13.365%   $226.2312   $226.23   $226.25   $226.20  
  Purchase #7 $207.77   13.346%   $235.499   $235.50   $235.50   $235.50  
  7 purchase totals = $931.38       $1,020.7714   $1,020.77   $1,020.75   $1,020.80