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	$158.33	5.142%	$166.4713	$166.47	$166.45	$166.50
Purchase #2	$57.69	3.133%	$59.4974	$59.50	$59.50	$59.50
Purchase #3	$116.38	7.403%	$124.9956	$125.00	$125.00	$125.00
Purchase #4	$15.99	10.573%	$17.6806	$17.68	$17.70	$17.70
Purchase #5	$79.72	12.646%	$89.8014	$89.80	$89.80	$89.80
Purchase #6	$136.64	12.857%	$154.2078	$154.21	$154.20	$154.20
Purchase #7	$173.66	13.305%	$196.7655	$196.77	$196.75	$196.80
7 purchase totals =	$738.41		$809.4196	$809.43	$809.40	$809.50