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	$144.85	13.441%	$164.3193	$164.32	$164.30	$164.30
Purchase #2	$131.62	3.408%	$136.1056	$136.11	$136.10	$136.10
Purchase #3	$43.27	12.714%	$48.7713	$48.77	$48.75	$48.80
Purchase #4	$61.95	6.419%	$65.9266	$65.93	$65.95	$65.90
Purchase #5	$40.99	3.597%	$42.4644	$42.46	$42.45	$42.50
Purchase #6	$5.96	3.720%	$6.1817	$6.18	$6.20	$6.20
Purchase #7	$83.97	7.756%	$90.4827	$90.48	$90.50	$90.50
7 purchase totals =	$512.61		$554.2516	$554.25	$554.25	$554.30