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	$44.26	12.494%	$49.7898	$49.79	$49.80	$49.80
Purchase #2	$39.73	9.650%	$43.5639	$43.56	$43.55	$43.60
Purchase #3	$19.87	5.551%	$20.973	$20.97	$20.95	$21.00
Purchase #4	$117.36	9.501%	$128.5104	$128.51	$128.50	$128.50
Purchase #5	$48.71	6.188%	$51.7242	$51.72	$51.70	$51.70
Purchase #6	$38.52	4.650%	$40.3112	$40.31	$40.30	$40.30
Purchase #7	$244.79	4.603%	$256.0577	$256.06	$256.05	$256.10
7 purchase totals =	$553.24		$590.9302	$590.92	$590.85	$591.00