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	$187.47	12.172%	$210.2888	$210.29	$210.30	$210.30
Purchase #2	$160.76	9.740%	$176.418	$176.42	$176.40	$176.40
Purchase #3	$121.29	12.308%	$136.2184	$136.22	$136.20	$136.20
Purchase #4	$122.78	13.824%	$139.7531	$139.75	$139.75	$139.80
Purchase #5	$89.84	11.599%	$100.2605	$100.26	$100.25	$100.30
Purchase #6	$228.43	4.369%	$238.4101	$238.41	$238.40	$238.40
Purchase #7	$96.32	11.845%	$107.7291	$107.73	$107.75	$107.70
7 purchase totals =	$1,006.89		$1,109.0780	$1,109.08	$1,109.05	$1,109.10