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	$45.32	4.148%	$47.1999	$47.20	$47.20	$47.20
Purchase #2	$121.45	7.128%	$130.107	$130.11	$130.10	$130.10
Purchase #3	$155.98	10.660%	$172.6075	$172.61	$172.60	$172.60
Purchase #4	$58.42	12.356%	$65.6384	$65.64	$65.65	$65.60
Purchase #5	$24.84	11.146%	$27.6087	$27.61	$27.60	$27.60
Purchase #6	$35.61	10.514%	$39.354	$39.35	$39.35	$39.40
Purchase #7	$95.32	5.746%	$100.7971	$100.80	$100.80	$100.80
7 purchase totals =	$536.94		$583.3126	$583.32	$583.30	$583.30