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	$74.84	10.658%	$82.8164	$82.82	$82.80	$82.80
Purchase #2	$245.74	10.815%	$272.3168	$272.32	$272.30	$272.30
Purchase #3	$31.40	3.283%	$32.4309	$32.43	$32.45	$32.40
Purchase #4	$93.65	11.685%	$104.593	$104.59	$104.60	$104.60
Purchase #5	$223.28	7.540%	$240.1153	$240.12	$240.10	$240.10
Purchase #6	$214.56	7.349%	$230.328	$230.33	$230.35	$230.30
Purchase #7	$118.52	10.584%	$131.0642	$131.06	$131.05	$131.10
7 purchase totals =	$1,001.99		$1,093.6646	$1,093.67	$1,093.65	$1,093.60