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	$90.57	10.728%	$100.2863	$100.29	$100.30	$100.30
Purchase #2	$82.42	6.534%	$87.8053	$87.81	$87.80	$87.80
Purchase #3	$188.45	6.405%	$200.5202	$200.52	$200.50	$200.50
Purchase #4	$162.74	8.225%	$176.1254	$176.13	$176.15	$176.10
Purchase #5	$62.60	13.469%	$71.0316	$71.03	$71.05	$71.00
Purchase #6	$89.81	6.828%	$95.9422	$95.94	$95.95	$95.90
Purchase #7	$245.94	4.760%	$257.6467	$257.65	$257.65	$257.60
7 purchase totals =	$922.53		$989.3577	$989.37	$989.40	$989.20