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	$20.56	4.524%	$21.4901	$21.49	$21.50	$21.50
Purchase #2	$73.64	8.210%	$79.6858	$79.69	$79.70	$79.70
Purchase #3	$12.40	12.797%	$13.9868	$13.99	$14.00	$14.00
Purchase #4	$137.57	6.333%	$146.2823	$146.28	$146.30	$146.30
Purchase #5	$160.52	5.854%	$169.9168	$169.92	$169.90	$169.90
Purchase #6	$81.81	8.842%	$89.0436	$89.04	$89.05	$89.00
Purchase #7	$224.46	13.631%	$255.0561	$255.06	$255.05	$255.10
7 purchase totals =	$710.96		$775.4615	$775.47	$775.50	$775.50