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	$209.40	4.726%	$219.2962	$219.30	$219.30	$219.30
Purchase #2	$150.43	10.237%	$165.8295	$165.83	$165.85	$165.80
Purchase #3	$211.50	12.485%	$237.9058	$237.91	$237.90	$237.90
Purchase #4	$130.39	10.347%	$143.8815	$143.88	$143.90	$143.90
Purchase #5	$91.52	9.587%	$100.294	$100.29	$100.30	$100.30
Purchase #6	$236.87	5.547%	$250.0092	$250.01	$250.00	$250.00
Purchase #7	$11.90	11.575%	$13.2774	$13.28	$13.30	$13.30
7 purchase totals =	$1,042.01		$1,130.4936	$1,130.50	$1,130.55	$1,130.50