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	$88.57	13.566%	$100.5854	$100.59	$100.60	$100.60
Purchase #2	$103.28	7.722%	$111.2553	$111.26	$111.25	$111.30
Purchase #3	$206.86	6.103%	$219.4847	$219.48	$219.50	$219.50
Purchase #4	$73.25	13.247%	$82.9534	$82.95	$82.95	$83.00
Purchase #5	$108.36	13.136%	$122.5942	$122.59	$122.60	$122.60
Purchase #6	$146.46	6.121%	$155.4248	$155.42	$155.40	$155.40
Purchase #7	$185.74	12.284%	$208.5563	$208.56	$208.55	$208.60
7 purchase totals =	$912.52		$1,000.8541	$1,000.85	$1,000.85	$1,001.00