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	$59.81	11.647%	$66.7761	$66.78	$66.80	$66.80
Purchase #2	$108.67	3.188%	$112.1344	$112.13	$112.15	$112.10
Purchase #3	$38.86	12.812%	$43.8387	$43.84	$43.85	$43.80
Purchase #4	$211.86	12.757%	$238.887	$238.89	$238.90	$238.90
Purchase #5	$125.61	12.730%	$141.6002	$141.60	$141.60	$141.60
Purchase #6	$166.55	6.139%	$176.7745	$176.77	$176.75	$176.80
Purchase #7	$147.50	7.330%	$158.3118	$158.31	$158.30	$158.30
7 purchase totals =	$858.86		$938.3227	$938.32	$938.35	$938.30