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	$107.63	9.314%	$117.6547	$117.65	$117.65	$117.70
Purchase #2	$85.79	4.103%	$89.31	$89.31	$89.30	$89.30
Purchase #3	$28.76	6.444%	$30.6133	$30.61	$30.60	$30.60
Purchase #4	$49.42	12.152%	$55.4255	$55.43	$55.45	$55.40
Purchase #5	$136.62	4.275%	$142.4605	$142.46	$142.45	$142.50
Purchase #6	$166.45	10.564%	$184.0338	$184.03	$184.05	$184.00
Purchase #7	$54.63	7.366%	$58.654	$58.65	$58.65	$58.70
7 purchase totals =	$629.30		$678.1518	$678.14	$678.15	$678.20