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	$139.63	13.632%	$158.6644	$158.66	$158.65	$158.70
Purchase #2	$37.45	12.321%	$42.0642	$42.06	$42.05	$42.10
Purchase #3	$106.65	5.145%	$112.1371	$112.14	$112.15	$112.10
Purchase #4	$6.86	9.621%	$7.52	$7.52	$7.50	$7.50
Purchase #5	$226.90	10.223%	$250.096	$250.10	$250.10	$250.10
Purchase #6	$18.66	6.668%	$19.9042	$19.90	$19.90	$19.90
Purchase #7	$204.56	13.710%	$232.6052	$232.61	$232.60	$232.60
7 purchase totals =	$740.71		$822.9911	$822.99	$822.95	$823.00