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	$117.44	9.335%	$128.403	$128.40	$128.40	$128.40
Purchase #2	$122.85	4.427%	$128.2886	$128.29	$128.30	$128.30
Purchase #3	$125.40	10.113%	$138.0817	$138.08	$138.10	$138.10
Purchase #4	$146.93	12.612%	$165.4608	$165.46	$165.45	$165.50
Purchase #5	$82.73	4.542%	$86.4876	$86.49	$86.50	$86.50
Purchase #6	$187.39	3.683%	$194.2916	$194.29	$194.30	$194.30
Purchase #7	$131.51	4.345%	$137.2241	$137.22	$137.20	$137.20
7 purchase totals =	$914.25		$978.2374	$978.23	$978.25	$978.30