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	$177.80	12.829%	$200.61	$200.61	$200.60	$200.60
Purchase #2	$17.99	3.504%	$18.6204	$18.62	$18.60	$18.60
Purchase #3	$61.40	9.726%	$67.3718	$67.37	$67.35	$67.40
Purchase #4	$94.97	8.874%	$103.3976	$103.40	$103.40	$103.40
Purchase #5	$204.76	8.227%	$221.6056	$221.61	$221.60	$221.60
Purchase #6	$169.70	7.120%	$181.7826	$181.78	$181.80	$181.80
Purchase #7	$233.35	9.807%	$256.2346	$256.23	$256.25	$256.20
7 purchase totals =	$959.97		$1,049.6226	$1,049.62	$1,049.60	$1,049.60