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	$210.71	13.567%	$239.297	$239.30	$239.30	$239.30
Purchase #2	$45.54	6.552%	$48.5238	$48.52	$48.50	$48.50
Purchase #3	$61.59	12.113%	$69.0504	$69.05	$69.05	$69.10
Purchase #4	$210.51	13.294%	$238.4952	$238.50	$238.50	$238.50
Purchase #5	$130.38	6.224%	$138.4949	$138.49	$138.50	$138.50
Purchase #6	$37.31	9.403%	$40.8183	$40.82	$40.80	$40.80
Purchase #7	$160.89	4.147%	$167.5621	$167.56	$167.55	$167.60
7 purchase totals =	$856.93		$942.2417	$942.24	$942.20	$942.30