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	$240.60	6.203%	$255.5244	$255.52	$255.50	$255.50
Purchase #2	$118.58	7.232%	$127.1557	$127.16	$127.15	$127.20
Purchase #3	$174.42	9.857%	$191.6126	$191.61	$191.60	$191.60
Purchase #4	$220.57	7.838%	$237.8583	$237.86	$237.85	$237.90
Purchase #5	$186.61	12.685%	$210.2815	$210.28	$210.30	$210.30
Purchase #6	$145.55	9.352%	$159.1618	$159.16	$159.15	$159.20
Purchase #7	$24.48	11.367%	$27.2626	$27.26	$27.25	$27.30
7 purchase totals =	$1,110.81		$1,208.8569	$1,208.85	$1,208.80	$1,209.00