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	$52.65	10.360%	$58.1045	$58.10	$58.10	$58.10
Purchase #2	$38.49	3.461%	$39.8221	$39.82	$39.80	$39.80
Purchase #3	$94.55	11.768%	$105.6766	$105.68	$105.70	$105.70
Purchase #4	$54.53	8.561%	$59.1983	$59.20	$59.20	$59.20
Purchase #5	$55.96	7.791%	$60.3198	$60.32	$60.30	$60.30
Purchase #6	$15.40	10.585%	$17.0301	$17.03	$17.05	$17.00
Purchase #7	$37.89	6.175%	$40.2297	$40.23	$40.25	$40.20
7 purchase totals =	$349.47		$380.3811	$380.38	$380.40	$380.30