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	$59.89	4.313%	$62.4731	$62.47	$62.45	$62.50
Purchase #2	$123.51	13.274%	$139.9047	$139.90	$139.90	$139.90
Purchase #3	$98.87	8.621%	$107.3936	$107.39	$107.40	$107.40
Purchase #4	$176.87	12.621%	$199.1928	$199.19	$199.20	$199.20
Purchase #5	$18.98	8.483%	$20.5901	$20.59	$20.60	$20.60
Purchase #6	$205.36	10.655%	$227.2411	$227.24	$227.25	$227.20
Purchase #7	$83.91	3.209%	$86.6027	$86.60	$86.60	$86.60
7 purchase totals =	$767.39		$843.3981	$843.38	$843.40	$843.40