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 $245.67   12.635%   $276.7104   $276.71   $276.70   $276.70  
  Purchase #2 $227.72   6.566%   $242.6721   $242.67   $242.65   $242.70  
  Purchase #3 $140.27   4.267%   $146.2553   $146.26   $146.25   $146.30  
  Purchase #4 $230.44   13.363%   $261.2337   $261.23   $261.25   $261.20  
  Purchase #5 $235.42   4.278%   $245.4913   $245.49   $245.50   $245.50  
  Purchase #6 $41.91   8.652%   $45.5361   $45.54   $45.55   $45.50  
  Purchase #7 $32.40   9.463%   $35.466   $35.47   $35.45   $35.50  
  7 purchase totals = $1,153.83       $1,253.3649   $1,253.37   $1,253.35   $1,253.40