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	$89.57	11.824%	$100.1608	$100.16	$100.15	$100.20
Purchase #2	$172.39	4.411%	$179.9941	$179.99	$180.00	$180.00
Purchase #3	$156.87	6.164%	$166.5395	$166.54	$166.55	$166.50
Purchase #4	$241.90	3.643%	$250.7124	$250.71	$250.70	$250.70
Purchase #5	$222.36	12.221%	$249.5346	$249.53	$249.55	$249.50
Purchase #6	$130.32	13.733%	$148.2168	$148.22	$148.20	$148.20
Purchase #7	$20.95	3.860%	$21.7587	$21.76	$21.75	$21.80
7 purchase totals =	$1,034.36		$1,116.9169	$1,116.91	$1,116.90	$1,116.90