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	$62.83	4.375%	$65.5788	$65.58	$65.60	$65.60
Purchase #2	$128.80	12.496%	$144.8948	$144.89	$144.90	$144.90
Purchase #3	$212.27	4.725%	$222.2998	$222.30	$222.30	$222.30
Purchase #4	$108.97	6.357%	$115.8972	$115.90	$115.90	$115.90
Purchase #5	$121.82	5.375%	$128.3678	$128.37	$128.35	$128.40
Purchase #6	$44.37	4.543%	$46.3857	$46.39	$46.40	$46.40
Purchase #7	$72.60	9.499%	$79.4963	$79.50	$79.50	$79.50
7 purchase totals =	$751.66		$802.9204	$802.93	$802.95	$803.00