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	$99.96	3.102%	$103.0608	$103.06	$103.05	$103.10
Purchase #2	$202.28	10.621%	$223.7642	$223.76	$223.75	$223.80
Purchase #3	$72.58	5.291%	$76.4202	$76.42	$76.40	$76.40
Purchase #4	$196.93	8.788%	$214.2362	$214.24	$214.25	$214.20
Purchase #5	$138.89	4.754%	$145.4928	$145.49	$145.50	$145.50
Purchase #6	$19.50	12.299%	$21.8983	$21.90	$21.90	$21.90
Purchase #7	$184.69	7.527%	$198.5916	$198.59	$198.60	$198.60
7 purchase totals =	$914.83		$983.4641	$983.46	$983.45	$983.50