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	$10.94	12.525%	$12.3102	$12.31	$12.30	$12.30
Purchase #2	$214.30	7.520%	$230.4154	$230.42	$230.40	$230.40
Purchase #3	$200.89	12.477%	$225.955	$225.96	$225.95	$226.00
Purchase #4	$102.45	8.463%	$111.1203	$111.12	$111.10	$111.10
Purchase #5	$219.52	10.306%	$242.1437	$242.14	$242.15	$242.10
Purchase #6	$106.28	3.357%	$109.8478	$109.85	$109.85	$109.80
Purchase #7	$80.25	12.293%	$90.1151	$90.12	$90.10	$90.10
7 purchase totals =	$934.63		$1,021.9075	$1,021.92	$1,021.85	$1,021.80