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	$19.51	12.528%	$21.9542	$21.95	$21.95	$22.00
Purchase #2	$138.92	13.791%	$158.0785	$158.08	$158.10	$158.10
Purchase #3	$240.64	6.782%	$256.9602	$256.96	$256.95	$257.00
Purchase #4	$98.57	4.561%	$103.0658	$103.07	$103.05	$103.10
Purchase #5	$178.79	12.333%	$200.8402	$200.84	$200.85	$200.80
Purchase #6	$167.78	10.263%	$184.9993	$185.00	$185.00	$185.00
Purchase #7	$29.25	7.631%	$31.4821	$31.48	$31.50	$31.50
7 purchase totals =	$873.46		$957.3803	$957.38	$957.40	$957.50