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	$248.75	13.172%	$281.5154	$281.52	$281.50	$281.50
Purchase #2	$38.60	9.231%	$42.1632	$42.16	$42.15	$42.20
Purchase #3	$167.41	6.555%	$178.3837	$178.38	$178.40	$178.40
Purchase #4	$10.30	12.399%	$11.5771	$11.58	$11.60	$11.60
Purchase #5	$216.55	11.853%	$242.2177	$242.22	$242.20	$242.20
Purchase #6	$40.25	8.108%	$43.5135	$43.51	$43.50	$43.50
Purchase #7	$239.68	10.760%	$265.4696	$265.47	$265.45	$265.50
7 purchase totals =	$961.54		$1,064.8402	$1,064.84	$1,064.80	$1,064.90