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	$243.71	13.846%	$277.4541	$277.45	$277.45	$277.50
Purchase #2	$78.83	3.475%	$81.5693	$81.57	$81.55	$81.60
Purchase #3	$64.86	13.357%	$73.5234	$73.52	$73.50	$73.50
Purchase #4	$170.39	3.241%	$175.9123	$175.91	$175.90	$175.90
Purchase #5	$37.46	3.367%	$38.7213	$38.72	$38.70	$38.70
Purchase #6	$127.54	7.468%	$137.0647	$137.06	$137.05	$137.10
Purchase #7	$206.44	13.595%	$234.5055	$234.51	$234.50	$234.50
7 purchase totals =	$929.23		$1,018.7506	$1,018.74	$1,018.65	$1,018.80