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	$32.68	3.806%	$33.9238	$33.92	$33.90	$33.90
Purchase #2	$40.94	7.319%	$43.9364	$43.94	$43.95	$43.90
Purchase #3	$145.93	3.230%	$150.6435	$150.64	$150.65	$150.60
Purchase #4	$146.53	12.131%	$164.3056	$164.31	$164.30	$164.30
Purchase #5	$205.34	6.178%	$218.0259	$218.03	$218.05	$218.00
Purchase #6	$205.92	9.293%	$225.0561	$225.06	$225.05	$225.10
Purchase #7	$230.91	4.797%	$241.9868	$241.99	$242.00	$242.00
7 purchase totals =	$1,008.25		$1,077.8781	$1,077.89	$1,077.90	$1,077.80