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	$15.98	8.359%	$17.3158	$17.32	$17.30	$17.30
Purchase #2	$71.25	10.819%	$78.9585	$78.96	$78.95	$79.00
Purchase #3	$176.40	11.244%	$196.2344	$196.23	$196.25	$196.20
Purchase #4	$109.68	8.342%	$118.8295	$118.83	$118.85	$118.80
Purchase #5	$103.70	6.490%	$110.4301	$110.43	$110.45	$110.40
Purchase #6	$129.84	9.497%	$142.1709	$142.17	$142.15	$142.20
Purchase #7	$132.47	9.805%	$145.4587	$145.46	$145.45	$145.50
7 purchase totals =	$739.32		$809.3979	$809.40	$809.40	$809.40