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	$217.67	11.339%	$242.3516	$242.35	$242.35	$242.40
Purchase #2	$233.72	13.638%	$265.5947	$265.59	$265.60	$265.60
Purchase #3	$123.46	12.800%	$139.2629	$139.26	$139.25	$139.30
Purchase #4	$20.65	7.285%	$22.1544	$22.15	$22.15	$22.20
Purchase #5	$15.50	11.224%	$17.2397	$17.24	$17.25	$17.20
Purchase #6	$53.84	11.627%	$60.1	$60.10	$60.10	$60.10
Purchase #7	$34.48	7.728%	$37.1446	$37.14	$37.15	$37.10
7 purchase totals =	$699.32		$783.8479	$783.83	$783.85	$783.90