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	$27.61	6.663%	$29.4497	$29.45	$29.45	$29.40
Purchase #2	$66.46	8.453%	$72.0779	$72.08	$72.10	$72.10
Purchase #3	$117.28	9.106%	$127.9595	$127.96	$127.95	$128.00
Purchase #4	$20.44	10.824%	$22.6524	$22.65	$22.65	$22.70
Purchase #5	$59.31	3.477%	$61.3722	$61.37	$61.35	$61.40
Purchase #6	$105.77	4.820%	$110.8681	$110.87	$110.85	$110.90
Purchase #7	$181.65	13.543%	$206.2509	$206.25	$206.25	$206.30
7 purchase totals =	$578.52		$630.6307	$630.63	$630.60	$630.80