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	$155.84	7.438%	$167.4314	$167.43	$167.45	$167.40
Purchase #2	$153.84	4.177%	$160.2659	$160.27	$160.25	$160.30
Purchase #3	$68.87	3.117%	$71.0167	$71.02	$71.00	$71.00
Purchase #4	$124.58	5.495%	$131.4257	$131.43	$131.45	$131.40
Purchase #5	$190.80	7.306%	$204.7398	$204.74	$204.75	$204.70
Purchase #6	$92.90	8.261%	$100.5745	$100.57	$100.55	$100.60
Purchase #7	$203.47	13.487%	$230.912	$230.91	$230.90	$230.90
7 purchase totals =	$990.30		$1,066.3660	$1,066.37	$1,066.35	$1,066.30