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	$98.68	7.804%	$106.381	$106.38	$106.40	$106.40
Purchase #2	$134.59	3.422%	$139.1957	$139.20	$139.20	$139.20
Purchase #3	$43.64	6.395%	$46.4308	$46.43	$46.45	$46.40
Purchase #4	$206.75	7.585%	$222.432	$222.43	$222.45	$222.40
Purchase #5	$81.74	11.861%	$91.4352	$91.44	$91.45	$91.40
Purchase #6	$46.34	5.143%	$48.7233	$48.72	$48.70	$48.70
Purchase #7	$17.58	13.839%	$20.0129	$20.01	$20.00	$20.00
7 purchase totals =	$629.32		$674.6109	$674.61	$674.65	$674.50