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	$240.39	13.569%	$273.0085	$273.01	$273.00	$273.00
Purchase #2	$41.96	9.841%	$46.0893	$46.09	$46.10	$46.10
Purchase #3	$19.87	7.143%	$21.2893	$21.29	$21.30	$21.30
Purchase #4	$37.81	9.724%	$41.4866	$41.49	$41.50	$41.50
Purchase #5	$97.72	11.456%	$108.9148	$108.91	$108.90	$108.90
Purchase #6	$158.41	13.164%	$179.2631	$179.26	$179.25	$179.30
Purchase #7	$77.54	5.589%	$81.8737	$81.87	$81.85	$81.90
7 purchase totals =	$673.70		$751.9253	$751.92	$751.90	$752.00