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	$34.99	10.796%	$38.7675	$38.77	$38.75	$38.80
Purchase #2	$178.84	10.788%	$198.1333	$198.13	$198.15	$198.10
Purchase #3	$111.30	10.610%	$123.1089	$123.11	$123.10	$123.10
Purchase #4	$148.44	3.377%	$153.4528	$153.45	$153.45	$153.50
Purchase #5	$127.61	13.787%	$145.2036	$145.20	$145.20	$145.20
Purchase #6	$33.46	11.244%	$37.2222	$37.22	$37.20	$37.20
Purchase #7	$26.41	5.801%	$27.942	$27.94	$27.95	$27.90
7 purchase totals =	$661.05		$723.8303	$723.82	$723.80	$723.80