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	$97.82	5.472%	$103.1727	$103.17	$103.15	$103.20
Purchase #2	$241.58	7.321%	$259.2661	$259.27	$259.25	$259.30
Purchase #3	$24.25	12.818%	$27.3584	$27.36	$27.35	$27.40
Purchase #4	$36.47	5.708%	$38.5517	$38.55	$38.55	$38.60
Purchase #5	$19.76	13.652%	$22.4576	$22.46	$22.45	$22.50
Purchase #6	$185.77	3.132%	$191.5883	$191.59	$191.60	$191.60
Purchase #7	$33.51	9.867%	$36.8164	$36.82	$36.80	$36.80
7 purchase totals =	$639.16		$679.2112	$679.22	$679.15	$679.40