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	$77.40	7.514%	$83.2158	$83.22	$83.20	$83.20
Purchase #2	$182.88	7.631%	$196.8356	$196.84	$196.85	$196.80
Purchase #3	$168.58	5.104%	$177.1843	$177.18	$177.20	$177.20
Purchase #4	$214.82	3.500%	$222.3387	$222.34	$222.35	$222.30
Purchase #5	$174.70	12.381%	$196.3296	$196.33	$196.35	$196.30
Purchase #6	$47.66	10.864%	$52.8378	$52.84	$52.85	$52.80
Purchase #7	$67.64	4.657%	$70.79	$70.79	$70.80	$70.80
7 purchase totals =	$933.68		$999.5318	$999.54	$999.60	$999.40