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	$56.84	7.804%	$61.2758	$61.28	$61.30	$61.30
Purchase #2	$118.40	4.770%	$124.0477	$124.05	$124.05	$124.00
Purchase #3	$83.37	6.807%	$89.045	$89.05	$89.05	$89.00
Purchase #4	$140.39	12.584%	$158.0567	$158.06	$158.05	$158.10
Purchase #5	$38.39	5.239%	$40.4013	$40.40	$40.40	$40.40
Purchase #6	$126.38	12.720%	$142.4555	$142.46	$142.45	$142.50
Purchase #7	$243.83	13.431%	$276.5788	$276.58	$276.60	$276.60
7 purchase totals =	$807.60		$891.8608	$891.88	$891.90	$891.90