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	$52.50	4.168%	$54.6882	$54.69	$54.70	$54.70
Purchase #2	$233.77	4.339%	$243.9133	$243.91	$243.90	$243.90
Purchase #3	$230.61	11.827%	$257.8842	$257.88	$257.90	$257.90
Purchase #4	$173.88	7.207%	$186.4115	$186.41	$186.40	$186.40
Purchase #5	$40.78	4.740%	$42.713	$42.71	$42.70	$42.70
Purchase #6	$111.73	13.162%	$126.4359	$126.44	$126.45	$126.40
Purchase #7	$116.44	11.756%	$130.1287	$130.13	$130.15	$130.10
7 purchase totals =	$959.71		$1,042.1748	$1,042.17	$1,042.20	$1,042.10