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	$5.91	5.418%	$6.2302	$6.23	$6.25	$6.20
Purchase #2	$130.58	10.357%	$144.1042	$144.10	$144.10	$144.10
Purchase #3	$211.82	10.408%	$233.8662	$233.87	$233.85	$233.90
Purchase #4	$109.92	10.864%	$121.8617	$121.86	$121.85	$121.90
Purchase #5	$103.30	5.607%	$109.092	$109.09	$109.10	$109.10
Purchase #6	$123.59	10.248%	$136.2555	$136.26	$136.25	$136.30
Purchase #7	$128.96	11.353%	$143.6008	$143.60	$143.60	$143.60
7 purchase totals =	$814.08		$895.0106	$895.01	$895.00	$895.10