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	$83.39	8.498%	$90.4765	$90.48	$90.50	$90.50
Purchase #2	$212.64	12.215%	$238.614	$238.61	$238.60	$238.60
Purchase #3	$30.69	3.230%	$31.6813	$31.68	$31.70	$31.70
Purchase #4	$233.52	5.105%	$245.4412	$245.44	$245.45	$245.40
Purchase #5	$6.49	10.520%	$7.1727	$7.17	$7.15	$7.20
Purchase #6	$69.75	6.422%	$74.2293	$74.23	$74.25	$74.20
Purchase #7	$38.90	6.701%	$41.5067	$41.51	$41.50	$41.50
7 purchase totals =	$675.38		$729.1217	$729.12	$729.15	$729.10