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	$35.52	6.150%	$37.7045	$37.70	$37.70	$37.70
Purchase #2	$19.78	7.401%	$21.2439	$21.24	$21.25	$21.20
Purchase #3	$79.77	7.806%	$85.9968	$86.00	$86.00	$86.00
Purchase #4	$174.53	3.313%	$180.3122	$180.31	$180.30	$180.30
Purchase #5	$21.43	8.631%	$23.2796	$23.28	$23.30	$23.30
Purchase #6	$52.82	6.142%	$56.0642	$56.06	$56.05	$56.10
Purchase #7	$244.38	4.663%	$255.7754	$255.78	$255.80	$255.80
7 purchase totals =	$628.23		$660.3766	$660.37	$660.40	$660.40