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	$137.99	7.622%	$148.5076	$148.51	$148.50	$148.50
Purchase #2	$231.54	8.741%	$251.7789	$251.78	$251.80	$251.80
Purchase #3	$148.58	4.446%	$155.1859	$155.19	$155.20	$155.20
Purchase #4	$223.63	6.789%	$238.8122	$238.81	$238.80	$238.80
Purchase #5	$182.74	4.257%	$190.5192	$190.52	$190.50	$190.50
Purchase #6	$42.37	3.501%	$43.8534	$43.85	$43.85	$43.90
Purchase #7	$177.81	5.669%	$187.89	$187.89	$187.90	$187.90
7 purchase totals =	$1,144.66		$1,216.5472	$1,216.55	$1,216.55	$1,216.60