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	$137.40	13.861%	$156.445	$156.45	$156.45	$156.40
Purchase #2	$82.33	7.726%	$88.6908	$88.69	$88.70	$88.70
Purchase #3	$192.71	13.805%	$219.3136	$219.31	$219.30	$219.30
Purchase #4	$176.87	8.277%	$191.5095	$191.51	$191.50	$191.50
Purchase #5	$101.39	11.286%	$112.8329	$112.83	$112.85	$112.80
Purchase #6	$233.33	13.689%	$265.2705	$265.27	$265.25	$265.30
Purchase #7	$83.42	6.181%	$88.5762	$88.58	$88.60	$88.60
7 purchase totals =	$1,007.45		$1,122.6385	$1,122.64	$1,122.65	$1,122.60