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	$143.39	7.256%	$153.7944	$153.79	$153.80	$153.80
Purchase #2	$175.69	6.845%	$187.716	$187.72	$187.70	$187.70
Purchase #3	$92.90	8.198%	$100.5159	$100.52	$100.50	$100.50
Purchase #4	$101.54	9.734%	$111.4239	$111.42	$111.40	$111.40
Purchase #5	$147.49	12.666%	$166.1711	$166.17	$166.15	$166.20
Purchase #6	$229.31	9.480%	$251.0486	$251.05	$251.05	$251.00
Purchase #7	$6.69	7.308%	$7.1789	$7.18	$7.20	$7.20
7 purchase totals =	$897.01		$977.8488	$977.85	$977.80	$977.80