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	$74.26	11.603%	$82.8764	$82.88	$82.90	$82.90
Purchase #2	$166.43	4.510%	$173.936	$173.94	$173.95	$173.90
Purchase #3	$177.71	8.146%	$192.1863	$192.19	$192.20	$192.20
Purchase #4	$180.97	10.770%	$200.4605	$200.46	$200.45	$200.50
Purchase #5	$81.41	11.438%	$90.7217	$90.72	$90.70	$90.70
Purchase #6	$211.90	7.128%	$227.0042	$227.00	$227.00	$227.00
Purchase #7	$187.35	9.498%	$205.1445	$205.14	$205.15	$205.10
7 purchase totals =	$1,080.03		$1,172.3296	$1,172.33	$1,172.35	$1,172.30