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	$233.69	3.766%	$242.4908	$242.49	$242.50	$242.50
Purchase #2	$164.43	7.754%	$177.1799	$177.18	$177.20	$177.20
Purchase #3	$120.69	11.154%	$134.1518	$134.15	$134.15	$134.20
Purchase #4	$208.50	10.508%	$230.4092	$230.41	$230.40	$230.40
Purchase #5	$71.80	8.835%	$78.1435	$78.14	$78.15	$78.10
Purchase #6	$156.39	11.841%	$174.9081	$174.91	$174.90	$174.90
Purchase #7	$89.72	10.389%	$99.041	$99.04	$99.05	$99.00
7 purchase totals =	$1,045.22		$1,136.3243	$1,136.32	$1,136.35	$1,136.30