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	$73.47	9.755%	$80.637	$80.64	$80.65	$80.60
Purchase #2	$228.43	4.225%	$238.0812	$238.08	$238.10	$238.10
Purchase #3	$44.31	5.137%	$46.5862	$46.59	$46.60	$46.60
Purchase #4	$104.42	4.171%	$108.7754	$108.78	$108.80	$108.80
Purchase #5	$60.96	3.229%	$62.9284	$62.93	$62.95	$62.90
Purchase #6	$158.90	6.677%	$169.5098	$169.51	$169.50	$169.50
Purchase #7	$48.61	9.774%	$53.3611	$53.36	$53.35	$53.40
7 purchase totals =	$719.10		$759.8791	$759.89	$759.95	$759.90