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	$54.79	8.736%	$59.5765	$59.58	$59.60	$59.60
Purchase #2	$103.27	12.469%	$116.1467	$116.15	$116.15	$116.10
Purchase #3	$185.76	13.116%	$210.1243	$210.12	$210.10	$210.10
Purchase #4	$235.39	12.387%	$264.5478	$264.55	$264.55	$264.50
Purchase #5	$166.50	4.352%	$173.7461	$173.75	$173.75	$173.70
Purchase #6	$142.27	4.530%	$148.7148	$148.71	$148.70	$148.70
Purchase #7	$92.58	10.609%	$102.4018	$102.40	$102.40	$102.40
7 purchase totals =	$980.56		$1,075.2580	$1,075.26	$1,075.25	$1,075.10