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	$134.25	3.754%	$139.2897	$139.29	$139.30	$139.30
Purchase #2	$102.39	11.174%	$113.8311	$113.83	$113.85	$113.80
Purchase #3	$211.56	6.245%	$224.7719	$224.77	$224.75	$224.80
Purchase #4	$92.52	11.857%	$103.4901	$103.49	$103.50	$103.50
Purchase #5	$38.35	7.646%	$41.2822	$41.28	$41.30	$41.30
Purchase #6	$217.77	5.564%	$229.8867	$229.89	$229.90	$229.90
Purchase #7	$9.49	10.640%	$10.4997	$10.50	$10.50	$10.50
7 purchase totals =	$806.33		$863.0514	$863.05	$863.10	$863.10