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	$11.52	13.596%	$13.0863	$13.09	$13.10	$13.10
Purchase #2	$105.73	10.498%	$116.8295	$116.83	$116.85	$116.80
Purchase #3	$56.79	11.107%	$63.0977	$63.10	$63.10	$63.10
Purchase #4	$113.70	12.459%	$127.8659	$127.87	$127.85	$127.90
Purchase #5	$141.81	13.182%	$160.5034	$160.50	$160.50	$160.50
Purchase #6	$33.69	8.354%	$36.5045	$36.50	$36.50	$36.50
Purchase #7	$55.49	13.534%	$63	$63.00	$63.00	$63.00
7 purchase totals =	$518.73		$580.8873	$580.89	$580.90	$580.90