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	$152.91	9.413%	$167.3034	$167.30	$167.30	$167.30
Purchase #2	$111.48	3.657%	$115.5568	$115.56	$115.55	$115.60
Purchase #3	$249.76	3.466%	$258.4167	$258.42	$258.40	$258.40
Purchase #4	$80.31	3.351%	$83.0012	$83.00	$83.00	$83.00
Purchase #5	$83.58	8.364%	$90.5706	$90.57	$90.55	$90.60
Purchase #6	$156.65	10.832%	$173.6183	$173.62	$173.60	$173.60
Purchase #7	$73.73	13.181%	$83.4484	$83.45	$83.45	$83.40
7 purchase totals =	$908.42		$971.9154	$971.92	$971.85	$971.90