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	$168.81	10.831%	$187.0938	$187.09	$187.10	$187.10
Purchase #2	$54.86	11.376%	$61.1009	$61.10	$61.10	$61.10
Purchase #3	$131.37	12.808%	$148.1959	$148.20	$148.20	$148.20
Purchase #4	$92.51	7.615%	$99.5546	$99.55	$99.55	$99.60
Purchase #5	$80.87	10.247%	$89.1567	$89.16	$89.15	$89.20
Purchase #6	$15.31	9.571%	$16.7753	$16.78	$16.80	$16.80
Purchase #7	$9.79	12.136%	$10.9781	$10.98	$11.00	$11.00
7 purchase totals =	$553.52		$612.8553	$612.86	$612.90	$613.00