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 $82.38   13.126%   $93.1932   $93.19   $93.20   $93.20  
  Purchase #2 $24.71   9.647%   $27.0938   $27.09   $27.10   $27.10  
  Purchase #3 $190.83   4.598%   $199.6044   $199.60   $199.60   $199.60  
  Purchase #4 $190.44   4.387%   $198.7946   $198.79   $198.80   $198.80  
  Purchase #5 $176.93   5.132%   $186.01   $186.01   $186.00   $186.00  
  Purchase #6 $93.72   5.308%   $98.6947   $98.69   $98.70   $98.70  
  Purchase #7 $18.90   8.850%   $20.5727   $20.57   $20.55   $20.60  
  7 purchase totals = $777.91       $823.9634   $823.94   $823.95   $824.00