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	$92.75	11.478%	$103.3958	$103.40	$103.40	$103.40
Purchase #2	$161.35	6.721%	$172.1943	$172.19	$172.20	$172.20
Purchase #3	$166.45	7.197%	$178.4294	$178.43	$178.45	$178.40
Purchase #4	$54.33	4.140%	$56.5793	$56.58	$56.60	$56.60
Purchase #5	$120.43	3.635%	$124.8076	$124.81	$124.80	$124.80
Purchase #6	$12.33	12.593%	$13.8827	$13.88	$13.90	$13.90
Purchase #7	$158.78	4.138%	$165.3503	$165.35	$165.35	$165.40
7 purchase totals =	$766.42		$814.6394	$814.64	$814.70	$814.70