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	$36.42	13.649%	$41.391	$41.39	$41.40	$41.40
Purchase #2	$115.84	10.337%	$127.8144	$127.81	$127.80	$127.80
Purchase #3	$224.54	4.158%	$233.8764	$233.88	$233.90	$233.90
Purchase #4	$158.64	8.232%	$171.6992	$171.70	$171.70	$171.70
Purchase #5	$219.79	10.763%	$243.446	$243.45	$243.45	$243.40
Purchase #6	$62.49	6.748%	$66.7068	$66.71	$66.70	$66.70
Purchase #7	$77.90	9.338%	$85.1743	$85.17	$85.15	$85.20
7 purchase totals =	$895.62		$970.1081	$970.11	$970.10	$970.10