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	$100.95	8.696%	$109.7286	$109.73	$109.75	$109.70
Purchase #2	$233.40	10.574%	$258.0797	$258.08	$258.10	$258.10
Purchase #3	$128.83	3.835%	$133.7706	$133.77	$133.75	$133.80
Purchase #4	$101.61	7.786%	$109.5214	$109.52	$109.50	$109.50
Purchase #5	$111.77	9.694%	$122.605	$122.61	$122.60	$122.60
Purchase #6	$116.44	6.303%	$123.7792	$123.78	$123.80	$123.80
Purchase #7	$37.34	12.631%	$42.0564	$42.06	$42.05	$42.10
7 purchase totals =	$830.34		$899.5409	$899.55	$899.55	$899.60