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	$148.79	10.668%	$164.6629	$164.66	$164.65	$164.70
Purchase #2	$51.95	7.776%	$55.9896	$55.99	$56.00	$56.00
Purchase #3	$101.78	9.149%	$111.0919	$111.09	$111.10	$111.10
Purchase #4	$127.66	9.216%	$139.4251	$139.43	$139.45	$139.40
Purchase #5	$145.79	6.279%	$154.9442	$154.94	$154.95	$154.90
Purchase #6	$51.64	9.385%	$56.4864	$56.49	$56.50	$56.50
Purchase #7	$223.83	6.560%	$238.5132	$238.51	$238.50	$238.50
7 purchase totals =	$851.44		$921.1133	$921.11	$921.15	$921.10