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	$105.91	11.286%	$117.863	$117.86	$117.85	$117.90
Purchase #2	$89.54	10.247%	$98.7152	$98.72	$98.70	$98.70
Purchase #3	$164.66	10.103%	$181.2956	$181.30	$181.30	$181.30
Purchase #4	$76.56	7.223%	$82.0899	$82.09	$82.10	$82.10
Purchase #5	$150.69	9.251%	$164.6303	$164.63	$164.65	$164.60
Purchase #6	$217.43	9.529%	$238.1489	$238.15	$238.15	$238.10
Purchase #7	$103.59	4.543%	$108.2961	$108.30	$108.30	$108.30
7 purchase totals =	$908.38		$991.0390	$991.05	$991.05	$991.00