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	$165.90	11.824%	$185.516	$185.52	$185.50	$185.50
Purchase #2	$193.58	12.369%	$217.5239	$217.52	$217.50	$217.50
Purchase #3	$104.37	5.795%	$110.4182	$110.42	$110.40	$110.40
Purchase #4	$164.80	8.334%	$178.5344	$178.53	$178.55	$178.50
Purchase #5	$39.93	11.746%	$44.6202	$44.62	$44.60	$44.60
Purchase #6	$181.27	9.784%	$199.0055	$199.01	$199.00	$199.00
Purchase #7	$50.31	9.613%	$55.1463	$55.15	$55.15	$55.10
7 purchase totals =	$900.16		$990.7645	$990.77	$990.70	$990.60