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	$158.65	12.860%	$179.0524	$179.05	$179.05	$179.10
Purchase #2	$151.84	12.225%	$170.4024	$170.40	$170.40	$170.40
Purchase #3	$103.66	7.640%	$111.5796	$111.58	$111.60	$111.60
Purchase #4	$70.40	13.795%	$80.1117	$80.11	$80.10	$80.10
Purchase #5	$87.51	3.446%	$90.5256	$90.53	$90.55	$90.50
Purchase #6	$166.88	3.814%	$173.2448	$173.24	$173.25	$173.20
Purchase #7	$36.25	12.536%	$40.7943	$40.79	$40.80	$40.80
7 purchase totals =	$775.19		$845.7108	$845.70	$845.75	$845.70