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	$160.87	6.819%	$171.8397	$171.84	$171.85	$171.80
Purchase #2	$246.77	4.710%	$258.3929	$258.39	$258.40	$258.40
Purchase #3	$81.52	7.466%	$87.6063	$87.61	$87.60	$87.60
Purchase #4	$200.73	12.497%	$225.8152	$225.82	$225.80	$225.80
Purchase #5	$25.26	9.301%	$27.6094	$27.61	$27.60	$27.60
Purchase #6	$18.39	10.513%	$20.3233	$20.32	$20.30	$20.30
Purchase #7	$241.71	3.543%	$250.2738	$250.27	$250.25	$250.30
7 purchase totals =	$975.25		$1,041.8606	$1,041.86	$1,041.80	$1,041.80