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	$139.84	3.224%	$144.3484	$144.35	$144.35	$144.30
Purchase #2	$147.38	3.762%	$152.9244	$152.92	$152.90	$152.90
Purchase #3	$109.44	6.773%	$116.8524	$116.85	$116.85	$116.90
Purchase #4	$230.63	12.668%	$259.8462	$259.85	$259.85	$259.80
Purchase #5	$59.64	12.720%	$67.2262	$67.23	$67.25	$67.20
Purchase #6	$21.35	5.870%	$22.6032	$22.60	$22.60	$22.60
Purchase #7	$89.83	3.119%	$92.6318	$92.63	$92.65	$92.60
7 purchase totals =	$798.11		$856.4326	$856.43	$856.45	$856.30