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	$123.65	12.840%	$139.5267	$139.53	$139.55	$139.50
Purchase #2	$188.85	13.545%	$214.4297	$214.43	$214.45	$214.40
Purchase #3	$53.91	9.829%	$59.2088	$59.21	$59.20	$59.20
Purchase #4	$60.91	11.354%	$67.8257	$67.83	$67.85	$67.80
Purchase #5	$221.29	7.446%	$237.7673	$237.77	$237.75	$237.80
Purchase #6	$103.56	10.591%	$114.528	$114.53	$114.55	$114.50
Purchase #7	$57.83	5.864%	$61.2212	$61.22	$61.20	$61.20
7 purchase totals =	$810.00		$894.5074	$894.52	$894.55	$894.40