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	$15.62	6.417%	$16.6223	$16.62	$16.60	$16.60
Purchase #2	$250.41	10.549%	$276.8258	$276.83	$276.85	$276.80
Purchase #3	$101.51	3.524%	$105.0872	$105.09	$105.10	$105.10
Purchase #4	$139.58	7.451%	$149.9801	$149.98	$150.00	$150.00
Purchase #5	$52.55	6.861%	$56.1555	$56.16	$56.15	$56.20
Purchase #6	$40.25	5.830%	$42.5966	$42.60	$42.60	$42.60
Purchase #7	$81.43	11.435%	$90.7415	$90.74	$90.75	$90.70
7 purchase totals =	$681.35		$738.0090	$738.02	$738.05	$738.00