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	$151.98	10.176%	$167.4455	$167.45	$167.45	$167.40
Purchase #2	$240.85	7.385%	$258.6368	$258.64	$258.65	$258.60
Purchase #3	$153.72	4.382%	$160.456	$160.46	$160.45	$160.50
Purchase #4	$47.90	12.342%	$53.8118	$53.81	$53.80	$53.80
Purchase #5	$18.82	5.559%	$19.8662	$19.87	$19.85	$19.90
Purchase #6	$28.82	8.388%	$31.2374	$31.24	$31.25	$31.20
Purchase #7	$181.58	3.231%	$187.4468	$187.45	$187.45	$187.40
7 purchase totals =	$823.67		$878.9005	$878.92	$878.90	$878.80