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 $62.78   9.768%   $68.9124   $68.91   $68.90   $68.90  
  Purchase #2 $193.87   7.201%   $207.8306   $207.83   $207.85   $207.80  
  Purchase #3 $173.41   8.351%   $187.8915   $187.89   $187.90   $187.90  
  Purchase #4 $111.70   6.742%   $119.2308   $119.23   $119.25   $119.20  
  Purchase #5 $246.82   12.176%   $276.8728   $276.87   $276.85   $276.90  
  Purchase #6 $120.88   3.575%   $125.2015   $125.20   $125.20   $125.20  
  Purchase #7 $72.95   11.735%   $81.5107   $81.51   $81.50   $81.50  
  7 purchase totals = $982.41       $1,067.4503   $1,067.44   $1,067.45   $1,067.40