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	$121.60	5.444%	$128.2199	$128.22	$128.20	$128.20
Purchase #2	$78.33	9.523%	$85.7894	$85.79	$85.80	$85.80
Purchase #3	$51.34	5.848%	$54.3424	$54.34	$54.35	$54.30
Purchase #4	$52.68	3.512%	$54.5301	$54.53	$54.55	$54.50
Purchase #5	$217.84	6.188%	$231.3199	$231.32	$231.30	$231.30
Purchase #6	$19.33	3.533%	$20.0129	$20.01	$20.00	$20.00
Purchase #7	$21.78	8.680%	$23.6705	$23.67	$23.65	$23.70
7 purchase totals =	$562.90		$597.8851	$597.88	$597.85	$597.80