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	$105.66	10.253%	$116.4933	$116.49	$116.50	$116.50
Purchase #2	$96.61	6.539%	$102.9273	$102.93	$102.95	$102.90
Purchase #3	$88.31	3.168%	$91.1077	$91.11	$91.10	$91.10
Purchase #4	$248.30	3.391%	$256.7199	$256.72	$256.70	$256.70
Purchase #5	$136.65	5.660%	$144.3844	$144.38	$144.40	$144.40
Purchase #6	$63.98	10.221%	$70.5194	$70.52	$70.50	$70.50
Purchase #7	$120.93	9.388%	$132.2829	$132.28	$132.30	$132.30
7 purchase totals =	$860.44		$914.4349	$914.43	$914.45	$914.40