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	$14.50	9.135%	$15.8246	$15.82	$15.80	$15.80
Purchase #2	$120.57	8.105%	$130.3422	$130.34	$130.35	$130.30
Purchase #3	$31.61	6.820%	$33.7658	$33.77	$33.75	$33.80
Purchase #4	$41.59	10.155%	$45.8135	$45.81	$45.80	$45.80
Purchase #5	$29.85	4.660%	$31.241	$31.24	$31.25	$31.20
Purchase #6	$247.51	13.235%	$280.2679	$280.27	$280.25	$280.30
Purchase #7	$144.83	5.681%	$153.0578	$153.06	$153.05	$153.10
7 purchase totals =	$630.46		$690.3128	$690.31	$690.25	$690.30