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	$18.63	7.461%	$20.02	$20.02	$20.00	$20.00
Purchase #2	$34.52	9.772%	$37.8933	$37.89	$37.90	$37.90
Purchase #3	$99.52	4.371%	$103.87	$103.87	$103.85	$103.90
Purchase #4	$77.87	10.765%	$86.2527	$86.25	$86.25	$86.30
Purchase #5	$44.58	8.308%	$48.2837	$48.28	$48.30	$48.30
Purchase #6	$80.41	6.245%	$85.4316	$85.43	$85.45	$85.40
Purchase #7	$76.94	10.121%	$84.7271	$84.73	$84.75	$84.70
7 purchase totals =	$432.47		$466.4784	$466.47	$466.50	$466.50