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	$47.46	8.410%	$51.4514	$51.45	$51.45	$51.50
Purchase #2	$149.69	5.572%	$158.0307	$158.03	$158.05	$158.00
Purchase #3	$15.52	10.566%	$17.1598	$17.16	$17.15	$17.20
Purchase #4	$78.59	5.282%	$82.7411	$82.74	$82.75	$82.70
Purchase #5	$122.97	4.359%	$128.3303	$128.33	$128.35	$128.30
Purchase #6	$101.83	12.111%	$114.1626	$114.16	$114.15	$114.20
Purchase #7	$90.76	12.264%	$101.8908	$101.89	$101.90	$101.90
7 purchase totals =	$606.82		$653.7667	$653.76	$653.80	$653.80