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	$225.42	4.378%	$235.2889	$235.29	$235.30	$235.30
Purchase #2	$132.99	7.462%	$142.9137	$142.91	$142.90	$142.90
Purchase #3	$158.57	6.209%	$168.4156	$168.42	$168.40	$168.40
Purchase #4	$129.47	10.129%	$142.584	$142.58	$142.60	$142.60
Purchase #5	$72.60	13.723%	$82.5629	$82.56	$82.55	$82.60
Purchase #6	$87.96	4.504%	$91.9217	$91.92	$91.90	$91.90
Purchase #7	$34.35	9.219%	$37.5167	$37.52	$37.50	$37.50
7 purchase totals =	$841.36		$901.2035	$901.20	$901.15	$901.20