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	$111.34	13.574%	$126.4533	$126.45	$126.45	$126.50
Purchase #2	$39.96	13.792%	$45.4713	$45.47	$45.45	$45.50
Purchase #3	$29.86	13.444%	$33.8744	$33.87	$33.85	$33.90
Purchase #4	$175.89	5.103%	$184.8657	$184.87	$184.85	$184.90
Purchase #5	$117.31	9.251%	$128.1623	$128.16	$128.15	$128.20
Purchase #6	$38.62	12.393%	$43.4062	$43.41	$43.40	$43.40
Purchase #7	$222.25	11.436%	$247.6665	$247.67	$247.65	$247.70
7 purchase totals =	$735.23		$809.8997	$809.90	$809.80	$810.10