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	$20.32	4.593%	$21.2533	$21.25	$21.25	$21.30
Purchase #2	$110.60	11.732%	$123.5756	$123.58	$123.60	$123.60
Purchase #3	$214.55	7.139%	$229.8667	$229.87	$229.85	$229.90
Purchase #4	$39.85	11.469%	$44.4204	$44.42	$44.40	$44.40
Purchase #5	$105.50	3.647%	$109.3476	$109.35	$109.35	$109.30
Purchase #6	$57.80	7.349%	$62.0477	$62.05	$62.05	$62.00
Purchase #7	$97.35	12.495%	$109.5139	$109.51	$109.50	$109.50
7 purchase totals =	$645.97		$700.0252	$700.03	$700.00	$700.00