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 $248.39   13.587%   $282.1387   $282.14   $282.15   $282.10  
  Purchase #2 $47.66   4.291%   $49.7051   $49.71   $49.70   $49.70  
  Purchase #3 $250.53   6.626%   $267.1301   $267.13   $267.15   $267.10  
  Purchase #4 $173.49   8.117%   $187.5722   $187.57   $187.55   $187.60  
  Purchase #5 $127.59   3.588%   $132.1679   $132.17   $132.15   $132.20  
  Purchase #6 $207.41   6.715%   $221.3376   $221.34   $221.35   $221.30  
  Purchase #7 $62.62   11.714%   $69.9553   $69.96   $69.95   $70.00  
  7 purchase totals = $1,117.69       $1,210.0069   $1,210.02   $1,210.00   $1,210.00