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	$66.54	8.516%	$72.2065	$72.21	$72.20	$72.20
Purchase #2	$203.44	13.260%	$230.4161	$230.42	$230.40	$230.40
Purchase #3	$5.89	3.482%	$6.0951	$6.10	$6.10	$6.10
Purchase #4	$186.77	13.245%	$211.5077	$211.51	$211.50	$211.50
Purchase #5	$50.36	4.400%	$52.5758	$52.58	$52.60	$52.60
Purchase #6	$128.49	12.870%	$145.0267	$145.03	$145.05	$145.00
Purchase #7	$100.76	10.439%	$111.2783	$111.28	$111.30	$111.30
7 purchase totals =	$742.25		$829.1062	$829.13	$829.15	$829.10