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	$169.56	6.323%	$180.2813	$180.28	$180.30	$180.30
Purchase #2	$37.49	12.292%	$42.0983	$42.10	$42.10	$42.10
Purchase #3	$64.91	4.267%	$67.6797	$67.68	$67.70	$67.70
Purchase #4	$137.40	9.753%	$150.8006	$150.80	$150.80	$150.80
Purchase #5	$189.52	5.322%	$199.6063	$199.61	$199.60	$199.60
Purchase #6	$74.62	7.753%	$80.4053	$80.41	$80.40	$80.40
Purchase #7	$43.26	8.275%	$46.8398	$46.84	$46.85	$46.80
7 purchase totals =	$716.76		$767.7113	$767.72	$767.75	$767.70