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 $218.96   7.464%   $235.3032   $235.30   $235.30   $235.30  
  Purchase #2 $74.98   10.608%   $82.9339   $82.93   $82.95   $82.90  
  Purchase #3 $219.66   13.797%   $249.9665   $249.97   $249.95   $250.00  
  Purchase #4 $212.26   6.121%   $225.2524   $225.25   $225.25   $225.30  
  Purchase #5 $105.56   5.543%   $111.4112   $111.41   $111.40   $111.40  
  Purchase #6 $110.45   8.562%   $119.9067   $119.91   $119.90   $119.90  
  Purchase #7 $192.82   11.247%   $214.5065   $214.51   $214.50   $214.50  
  7 purchase totals = $1,134.69       $1,239.2804   $1,239.28   $1,239.25   $1,239.30