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	$152.69	8.706%	$165.9832	$165.98	$166.00	$166.00
Purchase #2	$19.30	3.780%	$20.0295	$20.03	$20.05	$20.00
Purchase #3	$179.71	9.304%	$196.4302	$196.43	$196.45	$196.40
Purchase #4	$165.80	10.513%	$183.2306	$183.23	$183.25	$183.20
Purchase #5	$172.30	5.173%	$181.2131	$181.21	$181.20	$181.20
Purchase #6	$46.75	9.608%	$51.2417	$51.24	$51.25	$51.20
Purchase #7	$89.40	6.176%	$94.9213	$94.92	$94.90	$94.90
7 purchase totals =	$825.95		$893.0496	$893.04	$893.10	$892.90