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	$68.90	11.790%	$77.0233	$77.02	$77.00	$77.00
Purchase #2	$128.33	4.863%	$134.5707	$134.57	$134.55	$134.60
Purchase #3	$106.61	4.165%	$111.0503	$111.05	$111.05	$111.10
Purchase #4	$223.93	11.383%	$249.42	$249.42	$249.40	$249.40
Purchase #5	$132.85	7.228%	$142.4524	$142.45	$142.45	$142.50
Purchase #6	$30.92	11.638%	$34.5185	$34.52	$34.50	$34.50
Purchase #7	$83.80	13.376%	$95.0091	$95.01	$95.00	$95.00
7 purchase totals =	$775.34		$844.0443	$844.04	$843.95	$844.10