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	$249.84	11.385%	$278.2843	$278.28	$278.30	$278.30
Purchase #2	$56.42	5.632%	$59.5976	$59.60	$59.60	$59.60
Purchase #3	$99.59	8.108%	$107.6648	$107.66	$107.65	$107.70
Purchase #4	$242.97	3.541%	$251.5736	$251.57	$251.55	$251.60
Purchase #5	$239.78	5.294%	$252.474	$252.47	$252.45	$252.50
Purchase #6	$18.36	10.609%	$20.3078	$20.31	$20.30	$20.30
Purchase #7	$78.98	8.603%	$85.7746	$85.77	$85.75	$85.80
7 purchase totals =	$985.94		$1,055.6767	$1,055.66	$1,055.60	$1,055.80