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	$62.77	12.154%	$70.3991	$70.40	$70.40	$70.40
Purchase #2	$102.38	9.187%	$111.7857	$111.79	$111.80	$111.80
Purchase #3	$52.27	13.747%	$59.4556	$59.46	$59.45	$59.50
Purchase #4	$99.77	5.547%	$105.3042	$105.30	$105.30	$105.30
Purchase #5	$81.89	4.646%	$85.6946	$85.69	$85.70	$85.70
Purchase #6	$165.34	3.286%	$170.7731	$170.77	$170.75	$170.80
Purchase #7	$64.65	10.130%	$71.199	$71.20	$71.20	$71.20
7 purchase totals =	$629.07		$674.6113	$674.61	$674.60	$674.70