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	$106.60	9.309%	$116.5234	$116.52	$116.50	$116.50
Purchase #2	$219.90	12.222%	$246.7762	$246.78	$246.80	$246.80
Purchase #3	$212.82	5.871%	$225.3147	$225.31	$225.30	$225.30
Purchase #4	$16.32	10.687%	$18.0641	$18.06	$18.05	$18.10
Purchase #5	$181.82	5.200%	$191.2746	$191.27	$191.25	$191.30
Purchase #6	$194.77	5.153%	$204.8065	$204.81	$204.80	$204.80
Purchase #7	$137.47	11.603%	$153.4206	$153.42	$153.40	$153.40
7 purchase totals =	$1,069.70		$1,156.1801	$1,156.17	$1,156.10	$1,156.20