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	$49.97	9.103%	$54.5188	$54.52	$54.50	$54.50
Purchase #2	$116.45	9.408%	$127.4056	$127.41	$127.40	$127.40
Purchase #3	$94.99	13.642%	$107.9485	$107.95	$107.95	$107.90
Purchase #4	$129.77	6.662%	$138.4153	$138.42	$138.40	$138.40
Purchase #5	$110.90	4.120%	$115.4691	$115.47	$115.45	$115.50
Purchase #6	$32.86	12.658%	$37.0194	$37.02	$37.00	$37.00
Purchase #7	$116.76	8.870%	$127.1166	$127.12	$127.10	$127.10
7 purchase totals =	$651.70		$707.8933	$707.91	$707.80	$707.80