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	$59.81	11.769%	$66.849	$66.85	$66.85	$66.80
Purchase #2	$79.26	12.789%	$89.3966	$89.40	$89.40	$89.40
Purchase #3	$57.60	3.358%	$59.5342	$59.53	$59.55	$59.50
Purchase #4	$158.77	10.353%	$175.2075	$175.21	$175.20	$175.20
Purchase #5	$24.45	9.365%	$26.7397	$26.74	$26.75	$26.70
Purchase #6	$157.94	7.619%	$169.9734	$169.97	$169.95	$170.00
Purchase #7	$42.92	9.190%	$46.8643	$46.86	$46.85	$46.90
7 purchase totals =	$580.75		$634.5647	$634.56	$634.55	$634.50