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	$237.64	13.687%	$270.1658	$270.17	$270.15	$270.20
Purchase #2	$54.78	3.166%	$56.5143	$56.51	$56.50	$56.50
Purchase #3	$207.43	3.252%	$214.1756	$214.18	$214.20	$214.20
Purchase #4	$151.91	13.635%	$172.6229	$172.62	$172.60	$172.60
Purchase #5	$65.42	3.328%	$67.5972	$67.60	$67.60	$67.60
Purchase #6	$117.81	12.797%	$132.8861	$132.89	$132.90	$132.90
Purchase #7	$207.47	12.613%	$233.6382	$233.64	$233.65	$233.60
7 purchase totals =	$1,042.46		$1,147.6001	$1,147.61	$1,147.60	$1,147.60