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	$137.65	5.779%	$145.6048	$145.60	$145.60	$145.60
Purchase #2	$39.39	4.772%	$41.2697	$41.27	$41.25	$41.30
Purchase #3	$6.69	3.405%	$6.9178	$6.92	$6.90	$6.90
Purchase #4	$111.92	8.580%	$121.5227	$121.52	$121.50	$121.50
Purchase #5	$25.59	6.794%	$27.3286	$27.33	$27.35	$27.30
Purchase #6	$180.27	4.623%	$188.6039	$188.60	$188.60	$188.60
Purchase #7	$94.81	5.749%	$100.2606	$100.26	$100.25	$100.30
7 purchase totals =	$596.32		$631.5081	$631.50	$631.45	$631.50