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	$129.37	9.390%	$141.5178	$141.52	$141.50	$141.50
Purchase #2	$43.33	13.354%	$49.1163	$49.12	$49.10	$49.10
Purchase #3	$62.61	13.764%	$71.2276	$71.23	$71.25	$71.20
Purchase #4	$56.85	9.211%	$62.0865	$62.09	$62.10	$62.10
Purchase #5	$117.27	3.363%	$121.2138	$121.21	$121.20	$121.20
Purchase #6	$104.39	6.637%	$111.3184	$111.32	$111.30	$111.30
Purchase #7	$124.59	5.671%	$131.6555	$131.66	$131.65	$131.70
7 purchase totals =	$638.41		$688.1359	$688.15	$688.10	$688.10