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	$36.29	12.332%	$40.7653	$40.77	$40.75	$40.80
Purchase #2	$155.63	12.212%	$174.6355	$174.64	$174.65	$174.60
Purchase #3	$32.90	5.765%	$34.7967	$34.80	$34.80	$34.80
Purchase #4	$131.81	5.686%	$139.3047	$139.30	$139.30	$139.30
Purchase #5	$57.51	3.601%	$59.5809	$59.58	$59.60	$59.60
Purchase #6	$109.85	5.541%	$115.9368	$115.94	$115.95	$115.90
Purchase #7	$98.59	11.185%	$109.6173	$109.62	$109.60	$109.60
7 purchase totals =	$622.58		$674.6372	$674.65	$674.65	$674.60