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	$95.63	3.810%	$99.2735	$99.27	$99.25	$99.30
Purchase #2	$133.57	8.201%	$144.5241	$144.52	$144.50	$144.50
Purchase #3	$134.56	6.315%	$143.0575	$143.06	$143.05	$143.10
Purchase #4	$74.53	5.806%	$78.8572	$78.86	$78.85	$78.90
Purchase #5	$188.72	5.417%	$198.943	$198.94	$198.95	$198.90
Purchase #6	$92.28	10.201%	$101.6935	$101.69	$101.70	$101.70
Purchase #7	$207.93	8.260%	$225.105	$225.11	$225.10	$225.10
7 purchase totals =	$927.22		$991.4538	$991.45	$991.40	$991.50