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	$96.79	3.371%	$100.0528	$100.05	$100.05	$100.10
Purchase #2	$38.84	7.579%	$41.7837	$41.78	$41.80	$41.80
Purchase #3	$18.27	11.536%	$20.3776	$20.38	$20.40	$20.40
Purchase #4	$87.93	8.799%	$95.667	$95.67	$95.65	$95.70
Purchase #5	$115.64	6.813%	$123.5186	$123.52	$123.50	$123.50
Purchase #6	$109.45	13.858%	$124.6176	$124.62	$124.60	$124.60
Purchase #7	$46.38	7.302%	$49.7667	$49.77	$49.75	$49.80
7 purchase totals =	$513.30		$555.7840	$555.79	$555.75	$555.90