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	$56.93	3.594%	$58.9761	$58.98	$59.00	$59.00
Purchase #2	$48.97	8.847%	$53.3024	$53.30	$53.30	$53.30
Purchase #3	$156.41	7.703%	$168.4583	$168.46	$168.45	$168.50
Purchase #4	$72.28	3.613%	$74.8915	$74.89	$74.90	$74.90
Purchase #5	$36.89	5.357%	$38.8662	$38.87	$38.85	$38.90
Purchase #6	$118.37	7.858%	$127.6715	$127.67	$127.65	$127.70
Purchase #7	$65.35	3.568%	$67.6817	$67.68	$67.70	$67.70
7 purchase totals =	$555.20		$589.8477	$589.85	$589.85	$590.00