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	$85.38	6.312%	$90.7692	$90.77	$90.75	$90.80
Purchase #2	$204.82	9.845%	$224.9845	$224.98	$225.00	$225.00
Purchase #3	$5.36	7.593%	$5.767	$5.77	$5.75	$5.80
Purchase #4	$5.42	3.162%	$5.5914	$5.59	$5.60	$5.60
Purchase #5	$56.43	10.729%	$62.4844	$62.48	$62.50	$62.50
Purchase #6	$59.35	3.526%	$61.4427	$61.44	$61.45	$61.40
Purchase #7	$64.91	7.412%	$69.7211	$69.72	$69.70	$69.70
7 purchase totals =	$481.67		$520.7603	$520.75	$520.75	$520.80