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	$82.83	8.451%	$89.83	$89.83	$89.85	$89.80
Purchase #2	$151.35	11.869%	$169.3137	$169.31	$169.30	$169.30
Purchase #3	$194.73	5.490%	$205.4207	$205.42	$205.40	$205.40
Purchase #4	$38.38	7.841%	$41.3894	$41.39	$41.40	$41.40
Purchase #5	$27.40	12.555%	$30.8401	$30.84	$30.85	$30.80
Purchase #6	$64.27	11.754%	$71.8243	$71.82	$71.80	$71.80
Purchase #7	$66.60	11.774%	$74.4415	$74.44	$74.45	$74.40
7 purchase totals =	$625.56		$683.0597	$683.05	$683.05	$682.90