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	$247.75	11.661%	$276.6401	$276.64	$276.65	$276.60
Purchase #2	$159.31	9.587%	$174.583	$174.58	$174.60	$174.60
Purchase #3	$109.55	7.771%	$118.0631	$118.06	$118.05	$118.10
Purchase #4	$52.54	13.462%	$59.6129	$59.61	$59.60	$59.60
Purchase #5	$114.31	4.736%	$119.7237	$119.72	$119.70	$119.70
Purchase #6	$244.73	13.686%	$278.2237	$278.22	$278.20	$278.20
Purchase #7	$212.96	10.531%	$235.3868	$235.39	$235.40	$235.40
7 purchase totals =	$1,141.15		$1,262.2333	$1,262.22	$1,262.20	$1,262.20