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	$13.38	12.215%	$15.0144	$15.01	$15.00	$15.00
Purchase #2	$59.34	10.374%	$65.4959	$65.50	$65.50	$65.50
Purchase #3	$138.82	4.614%	$145.2252	$145.23	$145.25	$145.20
Purchase #4	$79.82	12.448%	$89.756	$89.76	$89.75	$89.80
Purchase #5	$45.45	6.787%	$48.5347	$48.53	$48.55	$48.50
Purchase #6	$48.70	12.449%	$54.7627	$54.76	$54.75	$54.80
Purchase #7	$205.64	12.524%	$231.3944	$231.39	$231.40	$231.40
7 purchase totals =	$591.15		$650.1833	$650.18	$650.20	$650.20