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	$99.95	9.637%	$109.5822	$109.58	$109.60	$109.60
Purchase #2	$98.53	5.258%	$103.7107	$103.71	$103.70	$103.70
Purchase #3	$146.39	9.714%	$160.6103	$160.61	$160.60	$160.60
Purchase #4	$51.78	11.275%	$57.6182	$57.62	$57.60	$57.60
Purchase #5	$170.42	10.197%	$187.7977	$187.80	$187.80	$187.80
Purchase #6	$82.45	12.511%	$92.7653	$92.77	$92.75	$92.80
Purchase #7	$9.75	5.605%	$10.2965	$10.30	$10.30	$10.30
7 purchase totals =	$659.27		$722.3809	$722.39	$722.35	$722.40