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	$51.73	5.136%	$54.3869	$54.39	$54.40	$54.40
Purchase #2	$43.55	3.297%	$44.9858	$44.99	$45.00	$45.00
Purchase #3	$129.83	12.759%	$146.395	$146.40	$146.40	$146.40
Purchase #4	$131.41	3.604%	$136.146	$136.15	$136.15	$136.10
Purchase #5	$233.81	13.546%	$265.4819	$265.48	$265.50	$265.50
Purchase #6	$232.38	9.807%	$255.1695	$255.17	$255.15	$255.20
Purchase #7	$158.77	9.156%	$173.307	$173.31	$173.30	$173.30
7 purchase totals =	$981.48		$1,075.8721	$1,075.89	$1,075.90	$1,075.90