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	$89.42	10.755%	$99.0371	$99.04	$99.05	$99.00
Purchase #2	$133.91	7.646%	$144.1488	$144.15	$144.15	$144.10
Purchase #3	$12.97	5.614%	$13.6981	$13.70	$13.70	$13.70
Purchase #4	$100.87	8.456%	$109.3996	$109.40	$109.40	$109.40
Purchase #5	$99.50	13.457%	$112.8897	$112.89	$112.90	$112.90
Purchase #6	$117.30	8.378%	$127.1274	$127.13	$127.15	$127.10
Purchase #7	$229.53	11.324%	$255.522	$255.52	$255.50	$255.50
7 purchase totals =	$783.50		$861.8227	$861.83	$861.85	$861.70