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	$115.74	11.819%	$129.4193	$129.42	$129.40	$129.40
Purchase #2	$32.59	5.657%	$34.4336	$34.43	$34.45	$34.40
Purchase #3	$225.74	10.783%	$250.0815	$250.08	$250.10	$250.10
Purchase #4	$21.62	4.743%	$22.6454	$22.65	$22.65	$22.60
Purchase #5	$164.93	12.420%	$185.4143	$185.41	$185.40	$185.40
Purchase #6	$158.27	4.545%	$165.4634	$165.46	$165.45	$165.50
Purchase #7	$82.33	8.340%	$89.1963	$89.20	$89.20	$89.20
7 purchase totals =	$801.22		$876.6538	$876.65	$876.65	$876.60