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	$30.74	8.657%	$33.4012	$33.40	$33.40	$33.40
Purchase #2	$154.91	8.534%	$168.13	$168.13	$168.15	$168.10
Purchase #3	$24.58	10.823%	$27.2403	$27.24	$27.25	$27.20
Purchase #4	$95.70	10.123%	$105.3877	$105.39	$105.40	$105.40
Purchase #5	$49.67	10.357%	$54.8143	$54.81	$54.80	$54.80
Purchase #6	$92.31	12.426%	$103.7804	$103.78	$103.80	$103.80
Purchase #7	$134.51	6.432%	$143.1617	$143.16	$143.15	$143.20
7 purchase totals =	$582.42		$635.9156	$635.91	$635.95	$635.90