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	$104.92	6.820%	$112.0755	$112.08	$112.10	$112.10
Purchase #2	$228.52	9.192%	$249.5256	$249.53	$249.55	$249.50
Purchase #3	$100.65	11.198%	$111.9208	$111.92	$111.90	$111.90
Purchase #4	$64.35	10.771%	$71.2811	$71.28	$71.30	$71.30
Purchase #5	$83.81	10.620%	$92.7106	$92.71	$92.70	$92.70
Purchase #6	$111.45	6.483%	$118.6753	$118.68	$118.70	$118.70
Purchase #7	$121.71	12.803%	$137.2925	$137.29	$137.30	$137.30
7 purchase totals =	$815.41		$893.4814	$893.49	$893.55	$893.50