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	$244.88	10.829%	$271.3981	$271.40	$271.40	$271.40
Purchase #2	$112.79	4.499%	$117.8644	$117.86	$117.85	$117.90
Purchase #3	$217.33	3.249%	$224.3911	$224.39	$224.40	$224.40
Purchase #4	$170.61	10.448%	$188.4353	$188.44	$188.45	$188.40
Purchase #5	$139.54	11.820%	$156.0336	$156.03	$156.05	$156.00
Purchase #6	$46.96	10.142%	$51.7227	$51.72	$51.70	$51.70
Purchase #7	$47.71	13.811%	$54.2992	$54.30	$54.30	$54.30
7 purchase totals =	$979.82		$1,064.1444	$1,064.14	$1,064.15	$1,064.10