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	$138.48	5.710%	$146.3872	$146.39	$146.40	$146.40
Purchase #2	$231.94	5.574%	$244.8683	$244.87	$244.85	$244.90
Purchase #3	$191.64	12.153%	$214.93	$214.93	$214.95	$214.90
Purchase #4	$184.46	10.860%	$204.4924	$204.49	$204.50	$204.50
Purchase #5	$143.50	13.323%	$162.6185	$162.62	$162.60	$162.60
Purchase #6	$102.73	8.323%	$111.2802	$111.28	$111.30	$111.30
Purchase #7	$31.79	3.164%	$32.7958	$32.80	$32.80	$32.80
7 purchase totals =	$1,024.54		$1,117.3724	$1,117.38	$1,117.40	$1,117.40