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	$131.61	9.533%	$144.1564	$144.16	$144.15	$144.20
Purchase #2	$28.68	6.761%	$30.6191	$30.62	$30.60	$30.60
Purchase #3	$111.35	4.410%	$116.2605	$116.26	$116.25	$116.30
Purchase #4	$40.88	6.469%	$43.5245	$43.52	$43.50	$43.50
Purchase #5	$74.75	7.173%	$80.1118	$80.11	$80.10	$80.10
Purchase #6	$50.53	3.674%	$52.3865	$52.39	$52.40	$52.40
Purchase #7	$28.96	6.830%	$30.938	$30.94	$30.95	$30.90
7 purchase totals =	$466.76		$497.9968	$498.00	$497.95	$498.00