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	$70.79	3.371%	$73.1763	$73.18	$73.20	$73.20
Purchase #2	$39.96	6.397%	$42.5162	$42.52	$42.50	$42.50
Purchase #3	$38.90	12.261%	$43.6695	$43.67	$43.65	$43.70
Purchase #4	$164.95	12.172%	$185.0277	$185.03	$185.05	$185.00
Purchase #5	$187.85	5.305%	$197.8154	$197.82	$197.80	$197.80
Purchase #6	$36.64	4.561%	$38.3112	$38.31	$38.30	$38.30
Purchase #7	$164.96	5.224%	$173.5775	$173.58	$173.60	$173.60
7 purchase totals =	$704.05		$754.0938	$754.11	$754.10	$754.10