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 $72.46   6.141%   $76.9098   $76.91   $76.90   $76.90  
  Purchase #2 $208.59   4.775%   $218.5502   $218.55   $218.55   $218.60  
  Purchase #3 $176.49   10.816%   $195.5792   $195.58   $195.60   $195.60  
  Purchase #4 $111.25   7.159%   $119.2144   $119.21   $119.20   $119.20  
  Purchase #5 $45.82   12.461%   $51.5296   $51.53   $51.55   $51.50  
  Purchase #6 $128.97   3.712%   $133.7574   $133.76   $133.75   $133.80  
  Purchase #7 $224.63   11.739%   $250.9993   $251.00   $251.00   $251.00  
  7 purchase totals = $968.21       $1,046.5399   $1,046.54   $1,046.55   $1,046.60