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	$72.72	8.865%	$79.1666	$79.17	$79.15	$79.20
Purchase #2	$84.32	7.805%	$90.9012	$90.90	$90.90	$90.90
Purchase #3	$105.55	7.827%	$113.8114	$113.81	$113.80	$113.80
Purchase #4	$13.76	13.576%	$15.6281	$15.63	$15.65	$15.60
Purchase #5	$207.38	13.546%	$235.4717	$235.47	$235.45	$235.50
Purchase #6	$89.94	6.291%	$95.5981	$95.60	$95.60	$95.60
Purchase #7	$17.53	12.732%	$19.7619	$19.76	$19.75	$19.80
7 purchase totals =	$591.20		$650.3390	$650.34	$650.30	$650.40