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	$92.46	8.717%	$100.5197	$100.52	$100.50	$100.50
Purchase #2	$231.81	9.619%	$254.1078	$254.11	$254.10	$254.10
Purchase #3	$100.77	8.501%	$109.3365	$109.34	$109.35	$109.30
Purchase #4	$24.88	9.394%	$27.2172	$27.22	$27.20	$27.20
Purchase #5	$43.27	11.418%	$48.2106	$48.21	$48.20	$48.20
Purchase #6	$104.43	11.529%	$116.4697	$116.47	$116.45	$116.50
Purchase #7	$138.95	3.508%	$143.8244	$143.82	$143.80	$143.80
7 purchase totals =	$736.57		$799.6859	$799.69	$799.60	$799.60