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	$74.40	5.557%	$78.5344	$78.53	$78.55	$78.50
Purchase #2	$89.48	9.679%	$98.1408	$98.14	$98.15	$98.10
Purchase #3	$84.70	6.714%	$90.3868	$90.39	$90.40	$90.40
Purchase #4	$60.83	4.250%	$63.4153	$63.42	$63.40	$63.40
Purchase #5	$228.94	6.566%	$243.9722	$243.97	$243.95	$244.00
Purchase #6	$216.67	8.670%	$235.4553	$235.46	$235.45	$235.50
Purchase #7	$21.81	11.665%	$24.3541	$24.35	$24.35	$24.40
7 purchase totals =	$776.83		$834.2589	$834.26	$834.25	$834.30