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	$156.30	3.693%	$162.0722	$162.07	$162.05	$162.10
Purchase #2	$37.86	4.304%	$39.4895	$39.49	$39.50	$39.50
Purchase #3	$137.67	5.844%	$145.7154	$145.72	$145.70	$145.70
Purchase #4	$17.91	11.753%	$20.015	$20.02	$20.00	$20.00
Purchase #5	$117.95	11.390%	$131.3845	$131.38	$131.40	$131.40
Purchase #6	$54.86	7.137%	$58.7754	$58.78	$58.80	$58.80
Purchase #7	$106.92	5.606%	$112.9139	$112.91	$112.90	$112.90
7 purchase totals =	$629.47		$670.3659	$670.37	$670.35	$670.40