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	$94.91	5.781%	$100.3967	$100.40	$100.40	$100.40
Purchase #2	$231.67	13.159%	$262.1555	$262.16	$262.15	$262.20
Purchase #3	$49.90	9.246%	$54.5138	$54.51	$54.50	$54.50
Purchase #4	$188.28	4.829%	$197.372	$197.37	$197.35	$197.40
Purchase #5	$105.53	5.715%	$111.561	$111.56	$111.55	$111.60
Purchase #6	$129.35	3.513%	$133.8941	$133.89	$133.90	$133.90
Purchase #7	$140.82	13.634%	$160.0194	$160.02	$160.00	$160.00
7 purchase totals =	$940.46		$1,019.9125	$1,019.91	$1,019.85	$1,020.00