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	$55.87	6.752%	$59.6423	$59.64	$59.65	$59.60
Purchase #2	$161.77	7.508%	$173.9157	$173.92	$173.90	$173.90
Purchase #3	$36.51	8.837%	$39.7364	$39.74	$39.75	$39.70
Purchase #4	$29.31	4.387%	$30.5958	$30.60	$30.60	$30.60
Purchase #5	$38.79	4.138%	$40.3951	$40.40	$40.40	$40.40
Purchase #6	$45.66	10.513%	$50.4602	$50.46	$50.45	$50.50
Purchase #7	$58.40	7.753%	$62.9278	$62.93	$62.95	$62.90
7 purchase totals =	$426.31		$457.6733	$457.69	$457.70	$457.60