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	$116.83	8.863%	$127.1846	$127.18	$127.20	$127.20
Purchase #2	$242.28	10.151%	$266.8738	$266.87	$266.85	$266.90
Purchase #3	$142.64	9.242%	$155.8228	$155.82	$155.80	$155.80
Purchase #4	$51.33	11.800%	$57.3869	$57.39	$57.40	$57.40
Purchase #5	$86.29	5.643%	$91.1593	$91.16	$91.15	$91.20
Purchase #6	$198.42	7.784%	$213.865	$213.87	$213.85	$213.90
Purchase #7	$79.32	3.268%	$81.9122	$81.91	$81.90	$81.90
7 purchase totals =	$917.11		$994.2046	$994.20	$994.15	$994.30