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	$73.32	11.271%	$81.5839	$81.58	$81.60	$81.60
Purchase #2	$74.88	4.561%	$78.2953	$78.30	$78.30	$78.30
Purchase #3	$168.67	4.555%	$176.3529	$176.35	$176.35	$176.40
Purchase #4	$241.77	13.781%	$275.0883	$275.09	$275.10	$275.10
Purchase #5	$81.87	9.444%	$89.6018	$89.60	$89.60	$89.60
Purchase #6	$43.41	6.304%	$46.1466	$46.15	$46.15	$46.10
Purchase #7	$31.68	4.267%	$33.0318	$33.03	$33.05	$33.00
7 purchase totals =	$715.60		$780.1006	$780.10	$780.15	$780.10