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	$89.62	12.157%	$100.5151	$100.52	$100.50	$100.50
Purchase #2	$92.42	10.667%	$102.2784	$102.28	$102.30	$102.30
Purchase #3	$171.71	6.812%	$183.4069	$183.41	$183.40	$183.40
Purchase #4	$213.63	5.358%	$225.0763	$225.08	$225.10	$225.10
Purchase #5	$40.89	4.326%	$42.6589	$42.66	$42.65	$42.70
Purchase #6	$13.73	10.308%	$15.1453	$15.15	$15.15	$15.10
Purchase #7	$134.52	4.849%	$141.0429	$141.04	$141.05	$141.00
7 purchase totals =	$756.52		$810.1238	$810.14	$810.15	$810.10