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	$50.65	11.118%	$56.2813	$56.28	$56.30	$56.30
Purchase #2	$77.63	12.261%	$87.1482	$87.15	$87.15	$87.10
Purchase #3	$96.85	6.835%	$103.4697	$103.47	$103.45	$103.50
Purchase #4	$123.87	10.677%	$137.0956	$137.10	$137.10	$137.10
Purchase #5	$202.59	3.597%	$209.8772	$209.88	$209.90	$209.90
Purchase #6	$250.88	11.495%	$279.7187	$279.72	$279.70	$279.70
Purchase #7	$125.60	9.585%	$137.6388	$137.64	$137.65	$137.60
7 purchase totals =	$928.07		$1,011.2295	$1,011.24	$1,011.25	$1,011.20