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	$31.61	6.439%	$33.6454	$33.65	$33.65	$33.60
Purchase #2	$99.57	3.480%	$103.035	$103.04	$103.05	$103.00
Purchase #3	$150.60	8.396%	$163.2444	$163.24	$163.25	$163.20
Purchase #4	$116.82	12.256%	$131.1375	$131.14	$131.15	$131.10
Purchase #5	$29.61	6.179%	$31.4396	$31.44	$31.45	$31.40
Purchase #6	$205.64	6.641%	$219.2966	$219.30	$219.30	$219.30
Purchase #7	$126.73	9.759%	$139.0976	$139.10	$139.10	$139.10
7 purchase totals =	$760.58		$820.8961	$820.91	$820.95	$820.70