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	$198.92	9.675%	$218.1655	$218.17	$218.15	$218.20
Purchase #2	$33.98	4.573%	$35.5339	$35.53	$35.55	$35.50
Purchase #3	$91.38	12.786%	$103.0638	$103.06	$103.05	$103.10
Purchase #4	$44.89	4.291%	$46.8162	$46.82	$46.80	$46.80
Purchase #5	$137.42	12.736%	$154.9218	$154.92	$154.90	$154.90
Purchase #6	$234.87	7.472%	$252.4195	$252.42	$252.40	$252.40
Purchase #7	$52.35	3.745%	$54.3105	$54.31	$54.30	$54.30
7 purchase totals =	$793.81		$865.2312	$865.23	$865.15	$865.20