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 $249.80   13.754%   $284.1575   $284.16   $284.15   $284.20  
  Purchase #2 $136.28   11.312%   $151.696   $151.70   $151.70   $151.70  
  Purchase #3 $7.39   4.647%   $7.7334   $7.73   $7.75   $7.70  
  Purchase #4 $119.33   5.172%   $125.5017   $125.50   $125.50   $125.50  
  Purchase #5 $222.96   6.552%   $237.5683   $237.57   $237.55   $237.60  
  Purchase #6 $96.63   5.364%   $101.8132   $101.81   $101.80   $101.80  
  Purchase #7 $112.54   6.200%   $119.5175   $119.52   $119.50   $119.50  
  7 purchase totals = $944.93       $1,027.9876   $1,027.99   $1,027.95   $1,028.00