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	$49.52	8.686%	$53.8213	$53.82	$53.80	$53.80
Purchase #2	$14.54	6.867%	$15.5385	$15.54	$15.55	$15.50
Purchase #3	$107.53	9.268%	$117.4959	$117.50	$117.50	$117.50
Purchase #4	$9.68	10.387%	$10.6855	$10.69	$10.70	$10.70
Purchase #5	$180.48	8.780%	$196.3261	$196.33	$196.35	$196.30
Purchase #6	$32.85	5.169%	$34.548	$34.55	$34.55	$34.50
Purchase #7	$89.32	3.705%	$92.6293	$92.63	$92.65	$92.60
7 purchase totals =	$483.92		$521.0446	$521.06	$521.10	$520.90