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 $213.72   11.141%   $237.5305   $237.53   $237.55   $237.50  
  Purchase #2 $144.52   8.680%   $157.0643   $157.06   $157.05   $157.10  
  Purchase #3 $192.33   13.804%   $218.8792   $218.88   $218.90   $218.90  
  Purchase #4 $67.86   8.616%   $73.7068   $73.71   $73.70   $73.70  
  Purchase #5 $138.49   13.179%   $156.7416   $156.74   $156.75   $156.70  
  Purchase #6 $88.27   11.437%   $98.3654   $98.37   $98.35   $98.40  
  Purchase #7 $74.54   10.324%   $82.2355   $82.24   $82.25   $82.20  
  7 purchase totals = $919.73       $1,024.5233   $1,024.53   $1,024.55   $1,024.50