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	$178.89	5.249%	$188.2799	$188.28	$188.30	$188.30
Purchase #2	$203.47	13.572%	$231.0849	$231.08	$231.10	$231.10
Purchase #3	$46.38	8.563%	$50.3515	$50.35	$50.35	$50.40
Purchase #4	$214.69	4.156%	$223.6125	$223.61	$223.60	$223.60
Purchase #5	$36.46	12.254%	$40.9278	$40.93	$40.95	$40.90
Purchase #6	$190.92	9.528%	$209.1109	$209.11	$209.10	$209.10
Purchase #7	$36.51	8.583%	$39.6437	$39.64	$39.65	$39.60
7 purchase totals =	$907.32		$983.0112	$983.00	$983.05	$983.00