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	$144.36	4.450%	$150.784	$150.78	$150.80	$150.80
Purchase #2	$40.90	6.254%	$43.4579	$43.46	$43.45	$43.50
Purchase #3	$40.59	5.542%	$42.8395	$42.84	$42.85	$42.80
Purchase #4	$112.62	10.864%	$124.855	$124.86	$124.85	$124.90
Purchase #5	$112.52	13.378%	$127.5729	$127.57	$127.55	$127.60
Purchase #6	$207.79	10.719%	$230.063	$230.06	$230.05	$230.10
Purchase #7	$250.52	3.796%	$260.0297	$260.03	$260.05	$260.00
7 purchase totals =	$909.30		$979.6020	$979.60	$979.60	$979.70