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	$39.82	11.454%	$44.381	$44.38	$44.40	$44.40
Purchase #2	$226.77	10.724%	$251.0888	$251.09	$251.10	$251.10
Purchase #3	$9.82	10.839%	$10.8844	$10.88	$10.90	$10.90
Purchase #4	$67.52	5.334%	$71.1215	$71.12	$71.10	$71.10
Purchase #5	$48.35	3.862%	$50.2173	$50.22	$50.20	$50.20
Purchase #6	$150.96	4.867%	$158.3072	$158.31	$158.30	$158.30
Purchase #7	$56.71	8.234%	$61.3795	$61.38	$61.40	$61.40
7 purchase totals =	$599.95		$647.3797	$647.38	$647.40	$647.40