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	$237.39	11.119%	$263.7854	$263.79	$263.80	$263.80
Purchase #2	$18.84	13.663%	$21.4141	$21.41	$21.40	$21.40
Purchase #3	$128.83	11.229%	$143.2963	$143.30	$143.30	$143.30
Purchase #4	$98.63	5.429%	$103.9846	$103.98	$104.00	$104.00
Purchase #5	$158.86	9.315%	$173.6578	$173.66	$173.65	$173.70
Purchase #6	$135.54	12.263%	$152.1613	$152.16	$152.15	$152.20
Purchase #7	$211.89	9.388%	$231.7822	$231.78	$231.80	$231.80
7 purchase totals =	$989.98		$1,090.0817	$1,090.08	$1,090.10	$1,090.20