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	$60.84	12.223%	$68.2765	$68.28	$68.30	$68.30
Purchase #2	$33.50	3.614%	$34.7107	$34.71	$34.70	$34.70
Purchase #3	$132.46	13.632%	$150.5169	$150.52	$150.50	$150.50
Purchase #4	$90.31	6.624%	$96.2921	$96.29	$96.30	$96.30
Purchase #5	$47.59	10.615%	$52.6417	$52.64	$52.65	$52.60
Purchase #6	$171.44	7.605%	$184.478	$184.48	$184.50	$184.50
Purchase #7	$109.55	6.340%	$116.4955	$116.50	$116.50	$116.50
7 purchase totals =	$645.69		$703.4114	$703.42	$703.45	$703.40