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	$113.52	12.526%	$127.7395	$127.74	$127.75	$127.70
Purchase #2	$136.44	5.676%	$144.1843	$144.18	$144.20	$144.20
Purchase #3	$127.76	3.792%	$132.6047	$132.60	$132.60	$132.60
Purchase #4	$36.33	12.680%	$40.9366	$40.94	$40.95	$40.90
Purchase #5	$206.27	10.252%	$227.4168	$227.42	$227.40	$227.40
Purchase #6	$131.77	11.290%	$146.6468	$146.65	$146.65	$146.60
Purchase #7	$92.36	3.302%	$95.4097	$95.41	$95.40	$95.40
7 purchase totals =	$844.45		$914.9384	$914.94	$914.95	$914.80