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	$95.88	5.873%	$101.511	$101.51	$101.50	$101.50
Purchase #2	$199.66	6.407%	$212.4522	$212.45	$212.45	$212.50
Purchase #3	$81.96	10.841%	$90.8453	$90.85	$90.85	$90.80
Purchase #4	$115.64	3.531%	$119.7232	$119.72	$119.70	$119.70
Purchase #5	$184.98	12.361%	$207.8454	$207.85	$207.85	$207.80
Purchase #6	$10.89	12.319%	$12.2315	$12.23	$12.25	$12.20
Purchase #7	$221.56	5.671%	$234.1247	$234.12	$234.10	$234.10
7 purchase totals =	$910.57		$978.7333	$978.73	$978.70	$978.60