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	$102.53	3.778%	$106.4036	$106.40	$106.40	$106.40
Purchase #2	$77.74	12.613%	$87.5453	$87.55	$87.55	$87.50
Purchase #3	$24.78	10.695%	$27.4302	$27.43	$27.45	$27.40
Purchase #4	$19.66	10.748%	$21.7731	$21.77	$21.75	$21.80
Purchase #5	$105.70	5.543%	$111.559	$111.56	$111.55	$111.60
Purchase #6	$94.56	13.567%	$107.389	$107.39	$107.40	$107.40
Purchase #7	$94.69	5.343%	$99.7493	$99.75	$99.75	$99.70
7 purchase totals =	$519.66		$561.8495	$561.85	$561.85	$561.80