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	$158.91	8.339%	$172.1615	$172.16	$172.15	$172.20
Purchase #2	$99.75	5.558%	$105.2941	$105.29	$105.30	$105.30
Purchase #3	$185.91	9.357%	$203.3056	$203.31	$203.30	$203.30
Purchase #4	$63.37	3.370%	$65.5056	$65.51	$65.50	$65.50
Purchase #5	$188.36	13.185%	$213.1953	$213.20	$213.20	$213.20
Purchase #6	$185.43	3.453%	$191.8329	$191.83	$191.85	$191.80
Purchase #7	$116.98	11.644%	$130.6012	$130.60	$130.60	$130.60
7 purchase totals =	$998.71		$1,081.8962	$1,081.90	$1,081.90	$1,081.90