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	$85.65	4.842%	$89.7972	$89.80	$89.80	$89.80
Purchase #2	$244.53	7.849%	$263.7232	$263.72	$263.70	$263.70
Purchase #3	$54.76	4.648%	$57.3052	$57.31	$57.30	$57.30
Purchase #4	$52.42	8.590%	$56.9229	$56.92	$56.90	$56.90
Purchase #5	$171.35	11.430%	$190.9353	$190.94	$190.95	$190.90
Purchase #6	$206.50	11.522%	$230.2929	$230.29	$230.30	$230.30
Purchase #7	$182.94	9.237%	$199.8382	$199.84	$199.85	$199.80
7 purchase totals =	$998.15		$1,088.8149	$1,088.82	$1,088.80	$1,088.70