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	$122.60	4.590%	$128.2273	$128.23	$128.25	$128.20
Purchase #2	$200.86	11.695%	$224.3506	$224.35	$224.35	$224.40
Purchase #3	$122.38	5.838%	$129.5245	$129.52	$129.50	$129.50
Purchase #4	$79.55	13.585%	$90.3569	$90.36	$90.35	$90.40
Purchase #5	$135.44	6.755%	$144.589	$144.59	$144.60	$144.60
Purchase #6	$138.28	7.418%	$148.5376	$148.54	$148.55	$148.50
Purchase #7	$212.66	8.362%	$230.4426	$230.44	$230.45	$230.40
7 purchase totals =	$1,011.77		$1,096.0285	$1,096.03	$1,096.05	$1,096.00