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	$31.36	6.476%	$33.3909	$33.39	$33.40	$33.40
Purchase #2	$116.32	13.443%	$131.9569	$131.96	$131.95	$132.00
Purchase #3	$151.92	13.701%	$172.7346	$172.73	$172.75	$172.70
Purchase #4	$240.91	12.676%	$271.4478	$271.45	$271.45	$271.40
Purchase #5	$18.27	13.656%	$20.765	$20.77	$20.75	$20.80
Purchase #6	$107.82	9.454%	$118.0133	$118.01	$118.00	$118.00
Purchase #7	$51.69	9.707%	$56.7075	$56.71	$56.70	$56.70
7 purchase totals =	$718.29		$805.0160	$805.02	$805.00	$805.00