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	$146.88	11.719%	$164.0929	$164.09	$164.10	$164.10
Purchase #2	$96.95	7.104%	$103.8373	$103.84	$103.85	$103.80
Purchase #3	$72.98	9.225%	$79.7124	$79.71	$79.70	$79.70
Purchase #4	$19.51	9.261%	$21.3168	$21.32	$21.30	$21.30
Purchase #5	$17.70	3.172%	$18.2614	$18.26	$18.25	$18.30
Purchase #6	$173.82	4.462%	$181.5758	$181.58	$181.60	$181.60
Purchase #7	$41.30	5.593%	$43.6099	$43.61	$43.60	$43.60
7 purchase totals =	$569.14		$612.4065	$612.41	$612.40	$612.40