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	$158.60	13.856%	$180.5756	$180.58	$180.60	$180.60
Purchase #2	$80.28	12.193%	$90.0685	$90.07	$90.05	$90.10
Purchase #3	$102.43	7.742%	$110.3601	$110.36	$110.35	$110.40
Purchase #4	$56.26	5.280%	$59.2305	$59.23	$59.25	$59.20
Purchase #5	$7.55	5.508%	$7.9659	$7.97	$7.95	$8.00
Purchase #6	$87.85	8.647%	$95.4464	$95.45	$95.45	$95.40
Purchase #7	$42.80	11.837%	$47.8662	$47.87	$47.85	$47.90
7 purchase totals =	$535.77		$591.5132	$591.53	$591.50	$591.60