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	$82.65	8.224%	$89.4471	$89.45	$89.45	$89.40
Purchase #2	$116.26	10.547%	$128.5219	$128.52	$128.50	$128.50
Purchase #3	$201.95	9.689%	$221.5169	$221.52	$221.50	$221.50
Purchase #4	$99.60	7.759%	$107.328	$107.33	$107.35	$107.30
Purchase #5	$96.42	13.134%	$109.0838	$109.08	$109.10	$109.10
Purchase #6	$25.89	8.575%	$28.1101	$28.11	$28.10	$28.10
Purchase #7	$11.89	4.116%	$12.3794	$12.38	$12.40	$12.40
7 purchase totals =	$634.66		$696.3872	$696.39	$696.40	$696.30