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	$100.28	12.511%	$112.826	$112.83	$112.85	$112.80
Purchase #2	$220.80	3.458%	$228.4353	$228.44	$228.45	$228.40
Purchase #3	$50.97	6.203%	$54.1317	$54.13	$54.15	$54.10
Purchase #4	$141.51	9.638%	$155.1487	$155.15	$155.15	$155.10
Purchase #5	$145.39	10.539%	$160.7127	$160.71	$160.70	$160.70
Purchase #6	$93.98	5.354%	$99.0117	$99.01	$99.00	$99.00
Purchase #7	$187.59	5.621%	$198.1344	$198.13	$198.15	$198.10
7 purchase totals =	$940.52		$1,008.4005	$1,008.40	$1,008.45	$1,008.20