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	$7.53	13.467%	$8.5441	$8.54	$8.55	$8.50
Purchase #2	$228.93	3.788%	$237.6019	$237.60	$237.60	$237.60
Purchase #3	$146.86	3.709%	$152.307	$152.31	$152.30	$152.30
Purchase #4	$60.65	9.781%	$66.5822	$66.58	$66.60	$66.60
Purchase #5	$40.81	3.267%	$42.1433	$42.14	$42.15	$42.10
Purchase #6	$20.53	7.649%	$22.1003	$22.10	$22.10	$22.10
Purchase #7	$127.55	4.144%	$132.8357	$132.84	$132.85	$132.80
7 purchase totals =	$632.86		$662.1145	$662.11	$662.15	$662.00