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 $218.87   11.479%   $243.9941   $243.99   $244.00   $244.00  
  Purchase #2 $85.86   13.281%   $97.2631   $97.26   $97.25   $97.30  
  Purchase #3 $76.99   13.710%   $87.5453   $87.55   $87.55   $87.50  
  Purchase #4 $113.66   8.504%   $123.3256   $123.33   $123.35   $123.30  
  Purchase #5 $69.90   8.852%   $76.0875   $76.09   $76.10   $76.10  
  Purchase #6 $242.93   6.674%   $259.1431   $259.14   $259.15   $259.10  
  Purchase #7 $8.51   8.598%   $9.2417   $9.24   $9.25   $9.20  
  7 purchase totals = $816.72       $896.6004   $896.60   $896.65   $896.50