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	$10.60	8.551%	$11.5064	$11.51	$11.50	$11.50
Purchase #2	$18.71	8.161%	$20.2369	$20.24	$20.25	$20.20
Purchase #3	$83.34	3.791%	$86.4994	$86.50	$86.50	$86.50
Purchase #4	$40.63	4.312%	$42.382	$42.38	$42.40	$42.40
Purchase #5	$136.34	6.169%	$144.7508	$144.75	$144.75	$144.80
Purchase #6	$118.49	6.356%	$126.0212	$126.02	$126.00	$126.00
Purchase #7	$18.63	12.573%	$20.9723	$20.97	$20.95	$21.00
7 purchase totals =	$426.74		$452.3690	$452.37	$452.35	$452.40