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	$45.87	6.321%	$48.7694	$48.77	$48.75	$48.80
Purchase #2	$128.56	11.121%	$142.8572	$142.86	$142.85	$142.90
Purchase #3	$111.46	5.253%	$117.315	$117.32	$117.30	$117.30
Purchase #4	$158.53	10.405%	$175.025	$175.03	$175.05	$175.00
Purchase #5	$210.84	6.621%	$224.7997	$224.80	$224.80	$224.80
Purchase #6	$198.63	3.331%	$205.2464	$205.25	$205.25	$205.20
Purchase #7	$63.72	4.538%	$66.6116	$66.61	$66.60	$66.60
7 purchase totals =	$917.61		$980.6243	$980.64	$980.60	$980.60