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	$221.86	6.773%	$236.8866	$236.89	$236.90	$236.90
Purchase #2	$99.71	12.300%	$111.9743	$111.97	$111.95	$112.00
Purchase #3	$108.85	13.797%	$123.868	$123.87	$123.85	$123.90
Purchase #4	$135.32	9.608%	$148.3215	$148.32	$148.30	$148.30
Purchase #5	$25.56	5.675%	$27.0105	$27.01	$27.00	$27.00
Purchase #6	$8.92	13.647%	$10.1373	$10.14	$10.15	$10.10
Purchase #7	$38.48	8.784%	$41.8601	$41.86	$41.85	$41.90
7 purchase totals =	$638.70		$700.0583	$700.06	$700.00	$700.10