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 $173.76   8.156%   $187.9319   $187.93   $187.95   $187.90  
  Purchase #2 $38.42   7.486%   $41.2961   $41.30   $41.30   $41.30  
  Purchase #3 $126.48   10.577%   $139.8578   $139.86   $139.85   $139.90  
  Purchase #4 $121.33   7.387%   $130.2926   $130.29   $130.30   $130.30  
  Purchase #5 $125.81   12.641%   $141.7136   $141.71   $141.70   $141.70  
  Purchase #6 $184.94   8.241%   $200.1809   $200.18   $200.20   $200.20  
  Purchase #7 $208.79   8.529%   $226.5977   $226.60   $226.60   $226.60  
  7 purchase totals = $979.53       $1,067.8706   $1,067.87   $1,067.90   $1,067.90