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	$197.77	12.500%	$222.4913	$222.49	$222.50	$222.50
Purchase #2	$18.69	3.657%	$19.3735	$19.37	$19.35	$19.40
Purchase #3	$107.38	10.647%	$118.8127	$118.81	$118.80	$118.80
Purchase #4	$141.88	12.673%	$159.8605	$159.86	$159.85	$159.90
Purchase #5	$127.58	13.202%	$144.4231	$144.42	$144.40	$144.40
Purchase #6	$54.31	6.805%	$58.0058	$58.01	$58.00	$58.00
Purchase #7	$227.28	9.823%	$249.6057	$249.61	$249.60	$249.60
7 purchase totals =	$874.89		$972.5726	$972.57	$972.50	$972.60