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	$16.70	3.491%	$17.283	$17.28	$17.30	$17.30
Purchase #2	$65.72	10.319%	$72.5016	$72.50	$72.50	$72.50
Purchase #3	$85.61	5.824%	$90.5959	$90.60	$90.60	$90.60
Purchase #4	$65.64	7.867%	$70.8039	$70.80	$70.80	$70.80
Purchase #5	$59.27	7.760%	$63.8694	$63.87	$63.85	$63.90
Purchase #6	$217.27	10.518%	$240.1225	$240.12	$240.10	$240.10
Purchase #7	$118.66	11.686%	$132.5266	$132.53	$132.55	$132.50
7 purchase totals =	$628.87		$687.7029	$687.70	$687.70	$687.70