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	$17.64	4.464%	$18.4274	$18.43	$18.45	$18.40
Purchase #2	$119.82	3.191%	$123.6435	$123.64	$123.65	$123.60
Purchase #3	$40.35	4.285%	$42.079	$42.08	$42.10	$42.10
Purchase #4	$139.83	5.291%	$147.2284	$147.23	$147.25	$147.20
Purchase #5	$56.53	8.526%	$61.3497	$61.35	$61.35	$61.30
Purchase #6	$36.32	13.602%	$41.2602	$41.26	$41.25	$41.30
Purchase #7	$203.36	4.136%	$211.771	$211.77	$211.75	$211.80
7 purchase totals =	$613.85		$645.7592	$645.76	$645.80	$645.70