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	$39.87	10.574%	$44.0859	$44.09	$44.10	$44.10
Purchase #2	$42.30	9.872%	$46.4759	$46.48	$46.50	$46.50
Purchase #3	$48.62	4.736%	$50.9226	$50.92	$50.90	$50.90
Purchase #4	$99.93	3.667%	$103.5944	$103.59	$103.60	$103.60
Purchase #5	$171.32	3.786%	$177.8062	$177.81	$177.80	$177.80
Purchase #6	$58.69	4.609%	$61.395	$61.40	$61.40	$61.40
Purchase #7	$11.89	5.447%	$12.5376	$12.54	$12.55	$12.50
7 purchase totals =	$472.62		$496.8176	$496.83	$496.85	$496.80