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	$9.88	10.259%	$10.8936	$10.89	$10.90	$10.90
Purchase #2	$9.32	7.698%	$10.0375	$10.04	$10.05	$10.00
Purchase #3	$123.67	10.345%	$136.4637	$136.46	$136.45	$136.50
Purchase #4	$243.88	5.689%	$257.7543	$257.75	$257.75	$257.80
Purchase #5	$39.29	9.121%	$42.8736	$42.87	$42.85	$42.90
Purchase #6	$51.46	9.298%	$56.2448	$56.24	$56.25	$56.20
Purchase #7	$78.66	4.587%	$82.2681	$82.27	$82.25	$82.30
7 purchase totals =	$556.16		$596.5356	$596.52	$596.50	$596.60