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	$111.93	10.479%	$123.6591	$123.66	$123.65	$123.70
Purchase #2	$237.95	5.432%	$250.8754	$250.88	$250.90	$250.90
Purchase #3	$28.47	3.730%	$29.5319	$29.53	$29.55	$29.50
Purchase #4	$16.69	6.846%	$17.8326	$17.83	$17.85	$17.80
Purchase #5	$100.67	7.231%	$107.9494	$107.95	$107.95	$107.90
Purchase #6	$25.53	4.104%	$26.5778	$26.58	$26.60	$26.60
Purchase #7	$100.79	10.546%	$111.4193	$111.42	$111.40	$111.40
7 purchase totals =	$622.03		$667.8455	$667.85	$667.90	$667.80