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	$82.72	7.564%	$88.9769	$88.98	$89.00	$89.00
Purchase #2	$153.62	9.464%	$168.1586	$168.16	$168.15	$168.20
Purchase #3	$225.55	8.584%	$244.9112	$244.91	$244.90	$244.90
Purchase #4	$140.29	7.123%	$150.2829	$150.28	$150.30	$150.30
Purchase #5	$59.85	7.603%	$64.4004	$64.40	$64.40	$64.40
Purchase #6	$117.87	8.384%	$127.7522	$127.75	$127.75	$127.80
Purchase #7	$21.45	7.786%	$23.1201	$23.12	$23.10	$23.10
7 purchase totals =	$801.35		$867.6023	$867.60	$867.60	$867.70