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	$169.54	6.172%	$180.004	$180.00	$180.00	$180.00
Purchase #2	$250.30	12.870%	$282.5136	$282.51	$282.50	$282.50
Purchase #3	$205.77	7.811%	$221.8427	$221.84	$221.85	$221.80
Purchase #4	$93.59	7.250%	$100.3753	$100.38	$100.40	$100.40
Purchase #5	$100.92	10.136%	$111.1493	$111.15	$111.15	$111.10
Purchase #6	$36.60	13.165%	$41.4184	$41.42	$41.40	$41.40
Purchase #7	$159.82	10.146%	$176.0353	$176.04	$176.05	$176.00
7 purchase totals =	$1,016.54		$1,113.3386	$1,113.34	$1,113.35	$1,113.20