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	$52.76	6.220%	$56.0417	$56.04	$56.05	$56.00
Purchase #2	$103.73	6.103%	$110.0606	$110.06	$110.05	$110.10
Purchase #3	$210.55	8.797%	$229.0721	$229.07	$229.05	$229.10
Purchase #4	$64.33	13.152%	$72.7907	$72.79	$72.80	$72.80
Purchase #5	$105.28	11.250%	$117.124	$117.12	$117.10	$117.10
Purchase #6	$83.72	13.794%	$95.2683	$95.27	$95.25	$95.30
Purchase #7	$34.89	9.129%	$38.0751	$38.08	$38.10	$38.10
7 purchase totals =	$655.26		$718.4325	$718.43	$718.40	$718.50