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	$49.61	13.255%	$56.1858	$56.19	$56.20	$56.20
Purchase #2	$201.56	5.832%	$213.315	$213.32	$213.30	$213.30
Purchase #3	$101.56	4.279%	$105.9058	$105.91	$105.90	$105.90
Purchase #4	$46.35	4.324%	$48.3542	$48.35	$48.35	$48.40
Purchase #5	$150.83	10.171%	$166.1709	$166.17	$166.15	$166.20
Purchase #6	$25.76	10.862%	$28.5581	$28.56	$28.55	$28.60
Purchase #7	$85.43	4.864%	$89.5853	$89.59	$89.60	$89.60
7 purchase totals =	$661.10		$708.0751	$708.09	$708.05	$708.20