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	$246.39	5.323%	$259.5053	$259.51	$259.50	$259.50
Purchase #2	$111.79	12.718%	$126.0075	$126.01	$126.00	$126.00
Purchase #3	$152.82	12.808%	$172.3932	$172.39	$172.40	$172.40
Purchase #4	$130.86	5.710%	$138.3321	$138.33	$138.35	$138.30
Purchase #5	$204.91	3.283%	$211.6372	$211.64	$211.65	$211.60
Purchase #6	$17.38	13.130%	$19.662	$19.66	$19.65	$19.70
Purchase #7	$69.68	3.394%	$72.0449	$72.04	$72.05	$72.00
7 purchase totals =	$933.83		$999.5822	$999.58	$999.60	$999.50