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	$11.73	6.602%	$12.5044	$12.50	$12.50	$12.50
Purchase #2	$174.96	13.589%	$198.7353	$198.74	$198.75	$198.70
Purchase #3	$173.76	6.361%	$184.8129	$184.81	$184.80	$184.80
Purchase #4	$219.71	9.872%	$241.3998	$241.40	$241.40	$241.40
Purchase #5	$166.40	4.401%	$173.7233	$173.72	$173.70	$173.70
Purchase #6	$27.68	5.593%	$29.2281	$29.23	$29.25	$29.20
Purchase #7	$78.46	13.504%	$89.0552	$89.06	$89.05	$89.10
7 purchase totals =	$852.70		$929.4590	$929.46	$929.45	$929.40