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	$88.52	12.851%	$99.8957	$99.90	$99.90	$99.90
Purchase #2	$182.45	7.485%	$196.1064	$196.11	$196.10	$196.10
Purchase #3	$166.29	5.311%	$175.1217	$175.12	$175.10	$175.10
Purchase #4	$222.59	8.550%	$241.6214	$241.62	$241.60	$241.60
Purchase #5	$162.69	6.678%	$173.5544	$173.55	$173.55	$173.60
Purchase #6	$27.65	3.457%	$28.6059	$28.61	$28.60	$28.60
Purchase #7	$158.66	4.866%	$166.3804	$166.38	$166.40	$166.40
7 purchase totals =	$1,008.85		$1,081.2859	$1,081.29	$1,081.25	$1,081.30