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	$78.30	4.798%	$82.0568	$82.06	$82.05	$82.10
Purchase #2	$185.46	5.193%	$195.0909	$195.09	$195.10	$195.10
Purchase #3	$139.49	12.276%	$156.6138	$156.61	$156.60	$156.60
Purchase #4	$104.74	13.183%	$118.5479	$118.55	$118.55	$118.50
Purchase #5	$102.26	13.704%	$116.2737	$116.27	$116.25	$116.30
Purchase #6	$196.69	10.671%	$217.6788	$217.68	$217.70	$217.70
Purchase #7	$94.62	10.242%	$104.311	$104.31	$104.30	$104.30
7 purchase totals =	$901.56		$990.5729	$990.57	$990.55	$990.60