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	$82.74	9.724%	$90.7856	$90.79	$90.80	$90.80
Purchase #2	$241.50	11.499%	$269.2701	$269.27	$269.25	$269.30
Purchase #3	$76.82	11.612%	$85.7403	$85.74	$85.75	$85.70
Purchase #4	$160.61	4.841%	$168.3851	$168.39	$168.40	$168.40
Purchase #5	$95.43	10.560%	$105.5074	$105.51	$105.50	$105.50
Purchase #6	$222.77	8.764%	$242.2936	$242.29	$242.30	$242.30
Purchase #7	$111.92	13.590%	$127.1299	$127.13	$127.15	$127.10
7 purchase totals =	$991.79		$1,089.1120	$1,089.12	$1,089.15	$1,089.10