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	$138.30	6.117%	$146.7598	$146.76	$146.75	$146.80
Purchase #2	$40.88	4.177%	$42.5876	$42.59	$42.60	$42.60
Purchase #3	$235.59	10.323%	$259.91	$259.91	$259.90	$259.90
Purchase #4	$95.35	4.114%	$99.2727	$99.27	$99.25	$99.30
Purchase #5	$123.84	5.344%	$130.458	$130.46	$130.45	$130.50
Purchase #6	$203.47	13.228%	$230.385	$230.39	$230.40	$230.40
Purchase #7	$42.75	6.675%	$45.6036	$45.60	$45.60	$45.60
7 purchase totals =	$880.18		$954.9767	$954.98	$954.95	$955.10