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	$132.48	10.377%	$146.2274	$146.23	$146.25	$146.20
Purchase #2	$34.60	7.268%	$37.1147	$37.11	$37.10	$37.10
Purchase #3	$157.31	5.641%	$166.1839	$166.18	$166.20	$166.20
Purchase #4	$236.71	9.686%	$259.6377	$259.64	$259.65	$259.60
Purchase #5	$85.73	5.824%	$90.7229	$90.72	$90.70	$90.70
Purchase #6	$8.74	11.762%	$9.768	$9.77	$9.75	$9.80
Purchase #7	$52.50	4.639%	$54.9355	$54.94	$54.95	$54.90
7 purchase totals =	$708.07		$764.5901	$764.59	$764.60	$764.50