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	$27.90	7.242%	$29.9205	$29.92	$29.90	$29.90
Purchase #2	$112.34	13.239%	$127.2127	$127.21	$127.20	$127.20
Purchase #3	$128.31	12.370%	$144.1819	$144.18	$144.20	$144.20
Purchase #4	$130.69	7.582%	$140.5989	$140.60	$140.60	$140.60
Purchase #5	$172.58	11.345%	$192.1592	$192.16	$192.15	$192.20
Purchase #6	$97.83	4.378%	$102.113	$102.11	$102.10	$102.10
Purchase #7	$140.68	8.555%	$152.7152	$152.72	$152.70	$152.70
7 purchase totals =	$810.33		$888.9014	$888.90	$888.85	$888.90