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 $239.36   4.407%   $249.9086   $249.91   $249.90   $249.90  
  Purchase #2 $209.29   8.324%   $226.7113   $226.71   $226.70   $226.70  
  Purchase #3 $114.52   8.670%   $124.4489   $124.45   $124.45   $124.40  
  Purchase #4 $186.26   6.495%   $198.3576   $198.36   $198.35   $198.40  
  Purchase #5 $135.31   4.357%   $141.2055   $141.21   $141.20   $141.20  
  Purchase #6 $120.25   11.242%   $133.7685   $133.77   $133.75   $133.80  
  Purchase #7 $113.87   10.599%   $125.9391   $125.94   $125.95   $125.90  
  7 purchase totals = $1,118.86       $1,200.3395   $1,200.35   $1,200.30   $1,200.30