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	$77.92	10.585%	$86.1678	$86.17	$86.15	$86.20
Purchase #2	$217.31	9.262%	$237.4373	$237.44	$237.45	$237.40
Purchase #3	$228.52	13.239%	$258.7738	$258.77	$258.75	$258.80
Purchase #4	$126.70	10.230%	$139.6614	$139.66	$139.65	$139.70
Purchase #5	$123.56	3.229%	$127.5498	$127.55	$127.55	$127.50
Purchase #6	$88.33	13.809%	$100.5275	$100.53	$100.55	$100.50
Purchase #7	$157.33	8.271%	$170.3428	$170.34	$170.35	$170.30
7 purchase totals =	$1,019.67		$1,120.4604	$1,120.46	$1,120.45	$1,120.40