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	$137.68	4.821%	$144.3176	$144.32	$144.30	$144.30
Purchase #2	$142.83	11.680%	$159.5125	$159.51	$159.50	$159.50
Purchase #3	$74.76	9.496%	$81.8592	$81.86	$81.85	$81.90
Purchase #4	$51.44	9.780%	$56.4708	$56.47	$56.45	$56.50
Purchase #5	$244.35	8.783%	$265.8113	$265.81	$265.80	$265.80
Purchase #6	$193.32	11.186%	$214.9448	$214.94	$214.95	$214.90
Purchase #7	$190.39	9.495%	$208.4675	$208.47	$208.45	$208.50
7 purchase totals =	$1,034.77		$1,131.3837	$1,131.38	$1,131.30	$1,131.40