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	$51.98	12.741%	$58.6028	$58.60	$58.60	$58.60
Purchase #2	$196.83	5.796%	$208.2383	$208.24	$208.25	$208.20
Purchase #3	$173.46	12.114%	$194.4729	$194.47	$194.45	$194.50
Purchase #4	$250.82	13.114%	$283.7125	$283.71	$283.70	$283.70
Purchase #5	$154.31	3.133%	$159.1445	$159.14	$159.15	$159.10
Purchase #6	$116.37	10.799%	$128.9368	$128.94	$128.95	$128.90
Purchase #7	$39.31	8.129%	$42.5055	$42.51	$42.50	$42.50
7 purchase totals =	$983.08		$1,075.6133	$1,075.61	$1,075.60	$1,075.50