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	$167.81	3.221%	$173.2152	$173.22	$173.20	$173.20
Purchase #2	$70.65	12.635%	$79.5766	$79.58	$79.60	$79.60
Purchase #3	$188.37	6.624%	$200.8476	$200.85	$200.85	$200.80
Purchase #4	$89.30	13.413%	$101.2778	$101.28	$101.30	$101.30
Purchase #5	$33.47	12.344%	$37.6015	$37.60	$37.60	$37.60
Purchase #6	$107.56	11.404%	$119.8261	$119.83	$119.85	$119.80
Purchase #7	$172.60	5.226%	$181.6201	$181.62	$181.60	$181.60
7 purchase totals =	$829.76		$893.9649	$893.98	$894.00	$893.90