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	$90.30	11.616%	$100.7892	$100.79	$100.80	$100.80
Purchase #2	$11.52	6.630%	$12.2838	$12.28	$12.30	$12.30
Purchase #3	$30.53	4.861%	$32.0141	$32.01	$32.00	$32.00
Purchase #4	$190.35	5.333%	$200.5014	$200.50	$200.50	$200.50
Purchase #5	$218.55	12.195%	$245.2022	$245.20	$245.20	$245.20
Purchase #6	$227.57	4.478%	$237.7606	$237.76	$237.75	$237.80
Purchase #7	$28.91	8.187%	$31.2769	$31.28	$31.30	$31.30
7 purchase totals =	$797.73		$859.8282	$859.82	$859.85	$859.90