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	$36.30	12.685%	$40.9047	$40.90	$40.90	$40.90
Purchase #2	$71.32	8.686%	$77.5149	$77.51	$77.50	$77.50
Purchase #3	$59.73	10.258%	$65.8571	$65.86	$65.85	$65.90
Purchase #4	$159.63	4.162%	$166.2738	$166.27	$166.25	$166.30
Purchase #5	$70.32	4.821%	$73.7101	$73.71	$73.70	$73.70
Purchase #6	$47.56	13.169%	$53.8232	$53.82	$53.80	$53.80
Purchase #7	$96.66	6.423%	$102.8685	$102.87	$102.85	$102.90
7 purchase totals =	$541.52		$580.9523	$580.94	$580.85	$581.00