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	$160.97	5.683%	$170.1179	$170.12	$170.10	$170.10
Purchase #2	$211.95	10.207%	$233.5837	$233.58	$233.60	$233.60
Purchase #3	$53.42	11.410%	$59.5152	$59.52	$59.50	$59.50
Purchase #4	$37.69	8.413%	$40.8609	$40.86	$40.85	$40.90
Purchase #5	$78.35	3.285%	$80.9238	$80.92	$80.90	$80.90
Purchase #6	$62.43	10.204%	$68.8004	$68.80	$68.80	$68.80
Purchase #7	$161.35	5.642%	$170.4534	$170.45	$170.45	$170.50
7 purchase totals =	$766.16		$824.2553	$824.25	$824.20	$824.30