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	$224.30	9.140%	$244.801	$244.80	$244.80	$244.80
Purchase #2	$237.56	7.266%	$254.8211	$254.82	$254.80	$254.80
Purchase #3	$100.47	4.708%	$105.2001	$105.20	$105.20	$105.20
Purchase #4	$202.77	13.624%	$230.3954	$230.40	$230.40	$230.40
Purchase #5	$168.87	3.805%	$175.2955	$175.30	$175.30	$175.30
Purchase #6	$150.93	10.493%	$166.7671	$166.77	$166.75	$166.80
Purchase #7	$59.39	3.731%	$61.6058	$61.61	$61.60	$61.60
7 purchase totals =	$1,144.29		$1,238.8860	$1,238.90	$1,238.85	$1,238.90