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	$18.68	7.439%	$20.0696	$20.07	$20.05	$20.10
Purchase #2	$159.32	12.183%	$178.73	$178.73	$178.75	$178.70
Purchase #3	$69.34	5.128%	$72.8958	$72.90	$72.90	$72.90
Purchase #4	$172.91	8.760%	$188.0569	$188.06	$188.05	$188.10
Purchase #5	$89.58	7.728%	$96.5027	$96.50	$96.50	$96.50
Purchase #6	$138.72	4.211%	$144.5615	$144.56	$144.55	$144.60
Purchase #7	$157.26	6.716%	$167.8216	$167.82	$167.80	$167.80
7 purchase totals =	$805.81		$868.6381	$868.64	$868.60	$868.70