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	$36.94	4.637%	$38.6529	$38.65	$38.65	$38.70
Purchase #2	$56.88	4.587%	$59.4891	$59.49	$59.50	$59.50
Purchase #3	$33.32	9.405%	$36.4537	$36.45	$36.45	$36.50
Purchase #4	$132.81	3.756%	$137.7983	$137.80	$137.80	$137.80
Purchase #5	$115.66	10.305%	$127.5788	$127.58	$127.60	$127.60
Purchase #6	$204.89	13.794%	$233.1525	$233.15	$233.15	$233.20
Purchase #7	$202.26	5.361%	$213.1032	$213.10	$213.10	$213.10
7 purchase totals =	$782.76		$846.2285	$846.22	$846.25	$846.40