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	$77.55	3.787%	$80.4868	$80.49	$80.50	$80.50
Purchase #2	$49.81	12.348%	$55.9605	$55.96	$55.95	$56.00
Purchase #3	$116.55	6.580%	$124.219	$124.22	$124.20	$124.20
Purchase #4	$152.83	12.849%	$172.4671	$172.47	$172.45	$172.50
Purchase #5	$60.99	7.621%	$65.638	$65.64	$65.65	$65.60
Purchase #6	$81.32	12.323%	$91.3411	$91.34	$91.35	$91.30
Purchase #7	$71.52	11.299%	$79.601	$79.60	$79.60	$79.60
7 purchase totals =	$610.57		$669.7135	$669.72	$669.70	$669.70