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	$162.50	6.177%	$172.5376	$172.54	$172.55	$172.50
Purchase #2	$53.90	12.824%	$60.8121	$60.81	$60.80	$60.80
Purchase #3	$39.89	9.526%	$43.6899	$43.69	$43.70	$43.70
Purchase #4	$9.74	10.762%	$10.7882	$10.79	$10.80	$10.80
Purchase #5	$146.88	12.713%	$165.5529	$165.55	$165.55	$165.60
Purchase #6	$99.42	6.228%	$105.6119	$105.61	$105.60	$105.60
Purchase #7	$137.99	8.564%	$149.8075	$149.81	$149.80	$149.80
7 purchase totals =	$650.32		$708.8001	$708.80	$708.80	$708.80