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	$34.56	12.607%	$38.917	$38.92	$38.90	$38.90
Purchase #2	$24.33	4.603%	$25.4499	$25.45	$25.45	$25.40
Purchase #3	$86.86	10.528%	$96.0046	$96.00	$96.00	$96.00
Purchase #4	$129.72	9.147%	$141.5855	$141.59	$141.60	$141.60
Purchase #5	$45.49	5.629%	$48.0506	$48.05	$48.05	$48.10
Purchase #6	$55.97	3.237%	$57.7817	$57.78	$57.80	$57.80
Purchase #7	$83.59	9.490%	$91.5227	$91.52	$91.50	$91.50
7 purchase totals =	$460.52		$499.3120	$499.31	$499.30	$499.30