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	$38.87	11.873%	$43.485	$43.49	$43.50	$43.50
Purchase #2	$244.91	12.503%	$275.5311	$275.53	$275.55	$275.50
Purchase #3	$133.47	10.548%	$147.5484	$147.55	$147.55	$147.50
Purchase #4	$44.42	9.207%	$48.5097	$48.51	$48.50	$48.50
Purchase #5	$92.75	12.413%	$104.2631	$104.26	$104.25	$104.30
Purchase #6	$107.28	3.491%	$111.0251	$111.03	$111.05	$111.00
Purchase #7	$110.29	8.107%	$119.2312	$119.23	$119.25	$119.20
7 purchase totals =	$771.99		$849.5936	$849.60	$849.65	$849.50