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	$230.81	7.730%	$248.6516	$248.65	$248.65	$248.70
Purchase #2	$48.94	9.260%	$53.4718	$53.47	$53.45	$53.50
Purchase #3	$74.89	10.418%	$82.692	$82.69	$82.70	$82.70
Purchase #4	$82.82	9.233%	$90.4668	$90.47	$90.45	$90.50
Purchase #5	$220.52	9.392%	$241.2312	$241.23	$241.25	$241.20
Purchase #6	$9.59	11.250%	$10.6689	$10.67	$10.65	$10.70
Purchase #7	$102.87	6.190%	$109.2377	$109.24	$109.25	$109.20
7 purchase totals =	$770.44		$836.4200	$836.42	$836.40	$836.50