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	$131.61	4.570%	$137.6246	$137.62	$137.60	$137.60
Purchase #2	$59.70	11.215%	$66.3954	$66.40	$66.40	$66.40
Purchase #3	$132.88	8.547%	$144.2373	$144.24	$144.25	$144.20
Purchase #4	$70.62	13.834%	$80.3896	$80.39	$80.40	$80.40
Purchase #5	$130.36	12.277%	$146.3643	$146.36	$146.35	$146.40
Purchase #6	$97.27	3.461%	$100.6365	$100.64	$100.65	$100.60
Purchase #7	$125.25	12.282%	$140.6332	$140.63	$140.65	$140.60
7 purchase totals =	$747.69		$816.2809	$816.28	$816.30	$816.20