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	$18.87	12.245%	$21.1806	$21.18	$21.20	$21.20
Purchase #2	$82.98	9.198%	$90.6125	$90.61	$90.60	$90.60
Purchase #3	$168.33	12.360%	$189.1356	$189.14	$189.15	$189.10
Purchase #4	$52.72	10.407%	$58.2066	$58.21	$58.20	$58.20
Purchase #5	$31.73	3.529%	$32.8498	$32.85	$32.85	$32.80
Purchase #6	$90.80	12.849%	$102.4669	$102.47	$102.45	$102.50
Purchase #7	$9.69	6.229%	$10.2936	$10.29	$10.30	$10.30
7 purchase totals =	$455.12		$504.7456	$504.75	$504.75	$504.70