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 $234.97   6.386%   $249.9752   $249.98   $250.00   $250.00  
  Purchase #2 $101.29   11.189%   $112.6233   $112.62   $112.60   $112.60  
  Purchase #3 $87.38   10.621%   $96.6606   $96.66   $96.65   $96.70  
  Purchase #4 $235.29   5.737%   $248.7886   $248.79   $248.80   $248.80  
  Purchase #5 $30.99   10.384%   $34.208   $34.21   $34.20   $34.20  
  Purchase #6 $136.73   5.788%   $144.6439   $144.64   $144.65   $144.60  
  Purchase #7 $216.38   4.387%   $225.8726   $225.87   $225.85   $225.90  
  7 purchase totals = $1,043.03       $1,112.7722   $1,112.77   $1,112.75   $1,112.80