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	$13.96	12.829%	$15.7509	$15.75	$15.75	$15.80
Purchase #2	$56.54	5.152%	$59.4529	$59.45	$59.45	$59.50
Purchase #3	$11.28	9.240%	$12.3223	$12.32	$12.30	$12.30
Purchase #4	$81.34	3.200%	$83.9429	$83.94	$83.95	$83.90
Purchase #5	$231.36	12.494%	$260.2661	$260.27	$260.25	$260.30
Purchase #6	$33.72	10.518%	$37.2667	$37.27	$37.25	$37.30
Purchase #7	$47.58	10.520%	$52.5854	$52.59	$52.60	$52.60
7 purchase totals =	$475.78		$521.5872	$521.59	$521.55	$521.70