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	$170.29	8.391%	$184.579	$184.58	$184.60	$184.60
Purchase #2	$96.31	12.680%	$108.5221	$108.52	$108.50	$108.50
Purchase #3	$85.57	13.238%	$96.8978	$96.90	$96.90	$96.90
Purchase #4	$144.66	7.381%	$155.3374	$155.34	$155.35	$155.30
Purchase #5	$47.54	12.786%	$53.6185	$53.62	$53.60	$53.60
Purchase #6	$27.29	4.196%	$28.4351	$28.44	$28.45	$28.40
Purchase #7	$59.52	9.608%	$65.2387	$65.24	$65.25	$65.20
7 purchase totals =	$631.18		$692.6286	$692.64	$692.65	$692.50