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	$55.27	12.567%	$62.2158	$62.22	$62.20	$62.20
Purchase #2	$121.25	8.812%	$131.9346	$131.93	$131.95	$131.90
Purchase #3	$94.76	11.259%	$105.429	$105.43	$105.45	$105.40
Purchase #4	$71.97	3.642%	$74.5911	$74.59	$74.60	$74.60
Purchase #5	$249.67	12.198%	$280.1247	$280.12	$280.10	$280.10
Purchase #6	$204.71	8.701%	$222.5218	$222.52	$222.50	$222.50
Purchase #7	$197.42	12.370%	$221.8409	$221.84	$221.85	$221.80
7 purchase totals =	$995.05		$1,098.6579	$1,098.65	$1,098.65	$1,098.50