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	$101.31	8.407%	$109.8271	$109.83	$109.85	$109.80
Purchase #2	$141.49	9.211%	$154.5226	$154.52	$154.50	$154.50
Purchase #3	$234.28	10.337%	$258.4975	$258.50	$258.50	$258.50
Purchase #4	$134.52	13.254%	$152.3493	$152.35	$152.35	$152.30
Purchase #5	$174.80	7.287%	$187.5377	$187.54	$187.55	$187.50
Purchase #6	$153.42	11.496%	$171.0572	$171.06	$171.05	$171.10
Purchase #7	$174.84	5.397%	$184.2761	$184.28	$184.30	$184.30
7 purchase totals =	$1,114.66		$1,218.0675	$1,218.08	$1,218.10	$1,218.00