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	$121.83	6.563%	$129.8257	$129.83	$129.85	$129.80
Purchase #2	$141.89	10.301%	$156.5061	$156.51	$156.50	$156.50
Purchase #3	$226.60	5.528%	$239.1264	$239.13	$239.15	$239.10
Purchase #4	$102.95	8.583%	$111.7862	$111.79	$111.80	$111.80
Purchase #5	$190.38	7.249%	$204.1806	$204.18	$204.20	$204.20
Purchase #6	$40.39	7.155%	$43.2799	$43.28	$43.30	$43.30
Purchase #7	$90.41	11.347%	$100.6688	$100.67	$100.65	$100.70
7 purchase totals =	$914.45		$985.3737	$985.39	$985.45	$985.40