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	$54.64	3.176%	$56.3754	$56.38	$56.40	$56.40
Purchase #2	$58.47	10.800%	$64.7848	$64.78	$64.80	$64.80
Purchase #3	$177.96	9.365%	$194.626	$194.63	$194.65	$194.60
Purchase #4	$91.45	9.635%	$100.2612	$100.26	$100.25	$100.30
Purchase #5	$172.93	10.720%	$191.4681	$191.47	$191.45	$191.50
Purchase #6	$205.42	13.370%	$232.8847	$232.88	$232.90	$232.90
Purchase #7	$63.87	11.827%	$71.4239	$71.42	$71.40	$71.40
7 purchase totals =	$824.74		$911.8241	$911.82	$911.85	$911.90