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	$183.81	4.793%	$192.62	$192.62	$192.60	$192.60
Purchase #2	$183.68	13.730%	$208.8993	$208.90	$208.90	$208.90
Purchase #3	$66.64	9.361%	$72.8782	$72.88	$72.90	$72.90
Purchase #4	$74.27	12.334%	$83.4305	$83.43	$83.45	$83.40
Purchase #5	$93.72	9.425%	$102.5531	$102.55	$102.55	$102.60
Purchase #6	$25.30	7.246%	$27.1332	$27.13	$27.15	$27.10
Purchase #7	$33.44	10.838%	$37.0642	$37.06	$37.05	$37.10
7 purchase totals =	$660.86		$724.5785	$724.57	$724.60	$724.60