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	$143.90	8.761%	$156.5071	$156.51	$156.50	$156.50
Purchase #2	$118.62	9.639%	$130.0538	$130.05	$130.05	$130.10
Purchase #3	$153.51	12.435%	$172.599	$172.60	$172.60	$172.60
Purchase #4	$249.72	4.760%	$261.6067	$261.61	$261.60	$261.60
Purchase #5	$208.48	5.234%	$219.3918	$219.39	$219.40	$219.40
Purchase #6	$175.87	7.379%	$188.8474	$188.85	$188.85	$188.80
Purchase #7	$129.62	10.736%	$143.536	$143.54	$143.55	$143.50
7 purchase totals =	$1,179.72		$1,272.5418	$1,272.55	$1,272.55	$1,272.50