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	$161.62	8.370%	$175.1476	$175.15	$175.15	$175.10
Purchase #2	$80.92	11.455%	$90.1894	$90.19	$90.20	$90.20
Purchase #3	$157.71	11.267%	$175.4792	$175.48	$175.50	$175.50
Purchase #4	$115.97	6.737%	$123.7829	$123.78	$123.80	$123.80
Purchase #5	$176.69	13.325%	$200.2339	$200.23	$200.25	$200.20
Purchase #6	$38.95	9.712%	$42.7328	$42.73	$42.75	$42.70
Purchase #7	$238.62	13.642%	$271.1725	$271.17	$271.15	$271.20
7 purchase totals =	$970.48		$1,078.7383	$1,078.73	$1,078.80	$1,078.70