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	$242.44	3.457%	$250.8212	$250.82	$250.80	$250.80
Purchase #2	$15.98	10.834%	$17.7113	$17.71	$17.70	$17.70
Purchase #3	$18.83	13.357%	$21.3451	$21.35	$21.35	$21.30
Purchase #4	$35.29	13.278%	$39.9758	$39.98	$40.00	$40.00
Purchase #5	$40.91	4.864%	$42.8999	$42.90	$42.90	$42.90
Purchase #6	$191.59	12.523%	$215.5828	$215.58	$215.60	$215.60
Purchase #7	$96.94	4.782%	$101.5757	$101.58	$101.60	$101.60
7 purchase totals =	$641.98		$689.9118	$689.92	$689.95	$689.90