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	$81.54	10.806%	$90.3512	$90.35	$90.35	$90.40
Purchase #2	$70.35	6.369%	$74.8306	$74.83	$74.85	$74.80
Purchase #3	$108.98	10.663%	$120.6005	$120.60	$120.60	$120.60
Purchase #4	$92.28	3.210%	$95.2422	$95.24	$95.25	$95.20
Purchase #5	$35.71	12.321%	$40.1098	$40.11	$40.10	$40.10
Purchase #6	$11.63	10.406%	$12.8402	$12.84	$12.85	$12.80
Purchase #7	$238.86	11.507%	$266.3456	$266.35	$266.35	$266.30
7 purchase totals =	$639.35		$700.3201	$700.32	$700.35	$700.20