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	$198.31	11.756%	$221.6233	$221.62	$221.60	$221.60
Purchase #2	$114.89	12.828%	$129.6281	$129.63	$129.65	$129.60
Purchase #3	$188.40	6.396%	$200.4501	$200.45	$200.45	$200.50
Purchase #4	$134.90	7.380%	$144.8556	$144.86	$144.85	$144.90
Purchase #5	$18.60	10.291%	$20.5141	$20.51	$20.50	$20.50
Purchase #6	$19.65	4.392%	$20.513	$20.51	$20.50	$20.50
Purchase #7	$49.74	6.263%	$52.8552	$52.86	$52.85	$52.90
7 purchase totals =	$724.49		$790.4394	$790.44	$790.40	$790.50