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	$91.73	13.628%	$104.231	$104.23	$104.25	$104.20
Purchase #2	$170.62	10.456%	$188.46	$188.46	$188.45	$188.50
Purchase #3	$17.69	10.218%	$19.4976	$19.50	$19.50	$19.50
Purchase #4	$183.50	10.837%	$203.3859	$203.39	$203.40	$203.40
Purchase #5	$19.50	10.679%	$21.5824	$21.58	$21.60	$21.60
Purchase #6	$47.64	7.143%	$51.0429	$51.04	$51.05	$51.00
Purchase #7	$104.78	4.822%	$109.8325	$109.83	$109.85	$109.80
7 purchase totals =	$635.46		$698.0323	$698.03	$698.10	$698.00