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	$131.80	8.848%	$143.4617	$143.46	$143.45	$143.50
Purchase #2	$89.39	12.797%	$100.8292	$100.83	$100.85	$100.80
Purchase #3	$21.83	6.708%	$23.2944	$23.29	$23.30	$23.30
Purchase #4	$177.33	4.484%	$185.2815	$185.28	$185.30	$185.30
Purchase #5	$248.76	11.384%	$277.0788	$277.08	$277.10	$277.10
Purchase #6	$226.87	10.249%	$250.1219	$250.12	$250.10	$250.10
Purchase #7	$23.40	7.499%	$25.1548	$25.15	$25.15	$25.20
7 purchase totals =	$919.38		$1,005.2223	$1,005.21	$1,005.25	$1,005.30