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	$47.98	6.874%	$51.2781	$51.28	$51.30	$51.30
Purchase #2	$79.90	11.858%	$89.3745	$89.37	$89.35	$89.40
Purchase #3	$153.80	9.342%	$168.168	$168.17	$168.15	$168.20
Purchase #4	$19.28	9.399%	$21.0921	$21.09	$21.10	$21.10
Purchase #5	$242.82	4.630%	$254.0626	$254.06	$254.05	$254.10
Purchase #6	$50.87	5.243%	$53.5371	$53.54	$53.55	$53.50
Purchase #7	$13.60	10.168%	$14.9828	$14.98	$15.00	$15.00
7 purchase totals =	$608.25		$652.4952	$652.49	$652.50	$652.60