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	$59.36	12.334%	$66.6815	$66.68	$66.70	$66.70
Purchase #2	$146.72	13.256%	$166.1692	$166.17	$166.15	$166.20
Purchase #3	$167.96	3.169%	$173.2827	$173.28	$173.30	$173.30
Purchase #4	$92.98	10.526%	$102.7671	$102.77	$102.75	$102.80
Purchase #5	$131.40	4.285%	$137.0305	$137.03	$137.05	$137.00
Purchase #6	$179.25	5.685%	$189.4404	$189.44	$189.45	$189.40
Purchase #7	$154.56	7.452%	$166.0778	$166.08	$166.10	$166.10
7 purchase totals =	$932.23		$1,001.4492	$1,001.45	$1,001.50	$1,001.50