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	$52.58	12.672%	$59.2429	$59.24	$59.25	$59.20
Purchase #2	$78.75	12.370%	$88.4914	$88.49	$88.50	$88.50
Purchase #3	$66.81	7.496%	$71.8181	$71.82	$71.80	$71.80
Purchase #4	$41.77	13.176%	$47.2736	$47.27	$47.25	$47.30
Purchase #5	$218.28	5.318%	$229.8881	$229.89	$229.90	$229.90
Purchase #6	$104.64	10.668%	$115.803	$115.80	$115.80	$115.80
Purchase #7	$16.74	10.845%	$18.5555	$18.56	$18.55	$18.60
7 purchase totals =	$579.57		$631.0726	$631.07	$631.05	$631.10