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	$105.75	13.839%	$120.3847	$120.38	$120.40	$120.40
Purchase #2	$185.58	4.840%	$194.5621	$194.56	$194.55	$194.60
Purchase #3	$48.79	10.189%	$53.7612	$53.76	$53.75	$53.80
Purchase #4	$81.94	10.497%	$90.5412	$90.54	$90.55	$90.50
Purchase #5	$111.78	6.565%	$119.1184	$119.12	$119.10	$119.10
Purchase #6	$89.64	12.382%	$100.7392	$100.74	$100.75	$100.70
Purchase #7	$59.76	4.372%	$62.3727	$62.37	$62.35	$62.40
7 purchase totals =	$683.24		$741.4795	$741.47	$741.45	$741.50