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	$249.88	8.164%	$270.2802	$270.28	$270.30	$270.30
Purchase #2	$103.52	7.112%	$110.8823	$110.88	$110.90	$110.90
Purchase #3	$28.79	12.697%	$32.4455	$32.45	$32.45	$32.40
Purchase #4	$83.51	4.426%	$87.2062	$87.21	$87.20	$87.20
Purchase #5	$205.81	4.711%	$215.5057	$215.51	$215.50	$215.50
Purchase #6	$20.35	5.719%	$21.5138	$21.51	$21.50	$21.50
Purchase #7	$64.59	6.194%	$68.5907	$68.59	$68.60	$68.60
7 purchase totals =	$756.45		$806.4244	$806.43	$806.45	$806.40