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	$39.37	3.457%	$40.731	$40.73	$40.75	$40.70
Purchase #2	$164.56	13.203%	$186.2869	$186.29	$186.30	$186.30
Purchase #3	$95.91	5.853%	$101.5236	$101.52	$101.50	$101.50
Purchase #4	$101.59	13.572%	$115.3778	$115.38	$115.40	$115.40
Purchase #5	$153.46	4.267%	$160.0081	$160.01	$160.00	$160.00
Purchase #6	$89.89	11.395%	$100.133	$100.13	$100.15	$100.10
Purchase #7	$139.25	9.587%	$152.5999	$152.60	$152.60	$152.60
7 purchase totals =	$784.03		$856.6603	$856.66	$856.70	$856.60