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	$129.39	7.714%	$139.3711	$139.37	$139.35	$139.40
Purchase #2	$235.71	4.714%	$246.8214	$246.82	$246.80	$246.80
Purchase #3	$115.37	13.827%	$131.3222	$131.32	$131.30	$131.30
Purchase #4	$88.40	13.870%	$100.6611	$100.66	$100.65	$100.70
Purchase #5	$100.29	9.166%	$109.4826	$109.48	$109.50	$109.50
Purchase #6	$81.89	5.130%	$86.091	$86.09	$86.10	$86.10
Purchase #7	$68.69	8.620%	$74.6111	$74.61	$74.60	$74.60
7 purchase totals =	$819.74		$888.3605	$888.35	$888.30	$888.40