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	$235.40	6.865%	$251.5602	$251.56	$251.55	$251.60
Purchase #2	$50.60	12.408%	$56.8784	$56.88	$56.90	$56.90
Purchase #3	$242.95	7.789%	$261.8734	$261.87	$261.85	$261.90
Purchase #4	$56.40	13.530%	$64.0309	$64.03	$64.05	$64.00
Purchase #5	$148.74	5.600%	$157.0694	$157.07	$157.05	$157.10
Purchase #6	$54.57	9.319%	$59.6554	$59.66	$59.65	$59.70
Purchase #7	$112.81	12.636%	$127.0647	$127.06	$127.05	$127.10
7 purchase totals =	$901.47		$978.1324	$978.13	$978.10	$978.30