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	$121.39	7.542%	$130.5452	$130.55	$130.55	$130.50
Purchase #2	$25.69	6.447%	$27.3462	$27.35	$27.35	$27.30
Purchase #3	$50.55	11.222%	$56.2227	$56.22	$56.20	$56.20
Purchase #4	$53.85	3.601%	$55.7891	$55.79	$55.80	$55.80
Purchase #5	$135.90	11.166%	$151.0746	$151.07	$151.05	$151.10
Purchase #6	$163.59	5.263%	$172.1997	$172.20	$172.20	$172.20
Purchase #7	$51.94	4.789%	$54.4274	$54.43	$54.45	$54.40
7 purchase totals =	$602.91		$647.6049	$647.61	$647.60	$647.50