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	$227.79	11.631%	$254.2843	$254.28	$254.30	$254.30
Purchase #2	$116.72	7.510%	$125.4857	$125.49	$125.50	$125.50
Purchase #3	$127.86	8.853%	$139.1794	$139.18	$139.20	$139.20
Purchase #4	$110.31	3.687%	$114.3771	$114.38	$114.40	$114.40
Purchase #5	$117.61	4.847%	$123.3106	$123.31	$123.30	$123.30
Purchase #6	$175.32	3.706%	$181.8174	$181.82	$181.80	$181.80
Purchase #7	$40.31	5.746%	$42.6262	$42.63	$42.65	$42.60
7 purchase totals =	$915.92		$981.0807	$981.09	$981.15	$981.10