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	$30.35	6.667%	$32.3734	$32.37	$32.35	$32.40
Purchase #2	$165.34	4.153%	$172.2066	$172.21	$172.20	$172.20
Purchase #3	$75.42	7.247%	$80.8857	$80.89	$80.90	$80.90
Purchase #4	$56.65	3.255%	$58.494	$58.49	$58.50	$58.50
Purchase #5	$12.78	13.537%	$14.51	$14.51	$14.50	$14.50
Purchase #6	$40.25	7.580%	$43.301	$43.30	$43.30	$43.30
Purchase #7	$173.33	8.711%	$188.4288	$188.43	$188.45	$188.40
7 purchase totals =	$554.12		$590.1995	$590.20	$590.20	$590.20