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	$9.79	8.183%	$10.5911	$10.59	$10.60	$10.60
Purchase #2	$10.99	7.869%	$11.8548	$11.85	$11.85	$11.90
Purchase #3	$124.73	9.427%	$136.4883	$136.49	$136.50	$136.50
Purchase #4	$29.48	12.745%	$33.2372	$33.24	$33.25	$33.20
Purchase #5	$169.58	7.688%	$182.6173	$182.62	$182.60	$182.60
Purchase #6	$184.30	6.599%	$196.462	$196.46	$196.45	$196.50
Purchase #7	$50.75	4.221%	$52.8922	$52.89	$52.90	$52.90
7 purchase totals =	$579.62		$624.1429	$624.14	$624.15	$624.20