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	$151.28	6.235%	$160.7123	$160.71	$160.70	$160.70
Purchase #2	$172.41	9.487%	$188.7665	$188.77	$188.75	$188.80
Purchase #3	$50.30	11.360%	$56.0141	$56.01	$56.00	$56.00
Purchase #4	$96.92	6.596%	$103.3128	$103.31	$103.30	$103.30
Purchase #5	$149.60	5.221%	$157.4106	$157.41	$157.40	$157.40
Purchase #6	$27.85	12.839%	$31.4257	$31.43	$31.45	$31.40
Purchase #7	$147.89	12.504%	$166.3822	$166.38	$166.40	$166.40
7 purchase totals =	$796.25		$864.0242	$864.02	$864.00	$864.00