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	$181.42	3.866%	$188.4337	$188.43	$188.45	$188.40
Purchase #2	$160.78	7.740%	$173.2244	$173.22	$173.20	$173.20
Purchase #3	$242.71	4.365%	$253.3043	$253.30	$253.30	$253.30
Purchase #4	$179.68	10.204%	$198.0145	$198.01	$198.00	$198.00
Purchase #5	$137.27	10.316%	$151.4308	$151.43	$151.45	$151.40
Purchase #6	$198.67	8.805%	$216.1629	$216.16	$216.15	$216.20
Purchase #7	$158.61	3.780%	$164.6055	$164.61	$164.60	$164.60
7 purchase totals =	$1,259.14		$1,345.1761	$1,345.16	$1,345.15	$1,345.10