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	$121.73	5.213%	$128.0758	$128.08	$128.10	$128.10
Purchase #2	$185.85	6.575%	$198.0696	$198.07	$198.05	$198.10
Purchase #3	$104.83	13.283%	$118.7546	$118.75	$118.75	$118.80
Purchase #4	$59.80	3.109%	$61.6592	$61.66	$61.65	$61.70
Purchase #5	$172.28	3.573%	$178.4356	$178.44	$178.45	$178.40
Purchase #6	$238.46	7.152%	$255.5147	$255.51	$255.50	$255.50
Purchase #7	$37.56	13.692%	$42.7027	$42.70	$42.70	$42.70
7 purchase totals =	$920.51		$983.2122	$983.21	$983.20	$983.30