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	$179.92	11.336%	$200.3157	$200.32	$200.30	$200.30
Purchase #2	$210.39	4.132%	$219.0833	$219.08	$219.10	$219.10
Purchase #3	$108.72	7.617%	$117.0012	$117.00	$117.00	$117.00
Purchase #4	$92.49	9.161%	$100.963	$100.96	$100.95	$101.00
Purchase #5	$145.76	5.539%	$153.8336	$153.83	$153.85	$153.80
Purchase #6	$37.53	3.497%	$38.8424	$38.84	$38.85	$38.80
Purchase #7	$30.26	10.646%	$33.4815	$33.48	$33.50	$33.50
7 purchase totals =	$805.07		$863.5207	$863.51	$863.55	$863.50