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	$126.66	6.245%	$134.5699	$134.57	$134.55	$134.60
Purchase #2	$97.44	9.222%	$106.4259	$106.43	$106.45	$106.40
Purchase #3	$110.31	11.671%	$123.1843	$123.18	$123.20	$123.20
Purchase #4	$153.61	13.835%	$174.8619	$174.86	$174.85	$174.90
Purchase #5	$36.71	4.835%	$38.4849	$38.48	$38.50	$38.50
Purchase #6	$96.98	6.370%	$103.1576	$103.16	$103.15	$103.20
Purchase #7	$17.42	12.526%	$19.602	$19.60	$19.60	$19.60
7 purchase totals =	$639.13		$700.2865	$700.28	$700.30	$700.40