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	$38.31	9.220%	$41.8422	$41.84	$41.85	$41.80
Purchase #2	$82.92	4.697%	$86.8148	$86.81	$86.80	$86.80
Purchase #3	$247.75	7.801%	$267.077	$267.08	$267.10	$267.10
Purchase #4	$132.72	8.728%	$144.3038	$144.30	$144.30	$144.30
Purchase #5	$28.96	10.287%	$31.9391	$31.94	$31.95	$31.90
Purchase #6	$84.82	7.817%	$91.4504	$91.45	$91.45	$91.50
Purchase #7	$96.76	8.716%	$105.1936	$105.19	$105.20	$105.20
7 purchase totals =	$712.24		$768.6209	$768.61	$768.65	$768.60