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	$79.51	7.432%	$85.4192	$85.42	$85.40	$85.40
Purchase #2	$99.72	5.466%	$105.1707	$105.17	$105.15	$105.20
Purchase #3	$107.32	4.234%	$111.8639	$111.86	$111.85	$111.90
Purchase #4	$198.70	5.140%	$208.9132	$208.91	$208.90	$208.90
Purchase #5	$250.87	9.757%	$275.3474	$275.35	$275.35	$275.30
Purchase #6	$163.58	3.157%	$168.7442	$168.74	$168.75	$168.70
Purchase #7	$243.98	8.787%	$265.4185	$265.42	$265.40	$265.40
7 purchase totals =	$1,143.68		$1,220.8771	$1,220.87	$1,220.80	$1,220.80