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	$211.61	13.571%	$240.3276	$240.33	$240.35	$240.30
Purchase #2	$24.51	10.580%	$27.1032	$27.10	$27.10	$27.10
Purchase #3	$144.98	6.626%	$154.5864	$154.59	$154.60	$154.60
Purchase #4	$60.56	10.856%	$67.1344	$67.13	$67.15	$67.10
Purchase #5	$53.69	11.503%	$59.866	$59.87	$59.85	$59.90
Purchase #6	$52.95	10.445%	$58.4806	$58.48	$58.50	$58.50
Purchase #7	$38.62	4.740%	$40.4506	$40.45	$40.45	$40.50
7 purchase totals =	$586.92		$647.9488	$647.95	$648.00	$648.00