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	$246.81	12.766%	$278.3178	$278.32	$278.30	$278.30
Purchase #2	$153.47	13.424%	$174.0718	$174.07	$174.05	$174.10
Purchase #3	$145.44	5.554%	$153.5177	$153.52	$153.50	$153.50
Purchase #4	$91.29	10.454%	$100.8335	$100.83	$100.85	$100.80
Purchase #5	$36.40	7.780%	$39.2319	$39.23	$39.25	$39.20
Purchase #6	$16.97	9.636%	$18.6052	$18.61	$18.60	$18.60
Purchase #7	$82.75	4.554%	$86.5184	$86.52	$86.50	$86.50
7 purchase totals =	$773.13		$851.0963	$851.10	$851.05	$851.00