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	$169.94	6.216%	$180.5035	$180.50	$180.50	$180.50
Purchase #2	$93.43	6.410%	$99.4189	$99.42	$99.40	$99.40
Purchase #3	$221.31	4.157%	$230.5099	$230.51	$230.50	$230.50
Purchase #4	$226.88	12.651%	$255.5826	$255.58	$255.60	$255.60
Purchase #5	$218.65	6.244%	$232.3025	$232.30	$232.30	$232.30
Purchase #6	$102.35	8.497%	$111.0467	$111.05	$111.05	$111.00
Purchase #7	$226.32	8.806%	$246.2497	$246.25	$246.25	$246.20
7 purchase totals =	$1,258.88		$1,355.6138	$1,355.61	$1,355.60	$1,355.50