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	$79.78	13.316%	$90.4035	$90.40	$90.40	$90.40
Purchase #2	$113.99	12.759%	$128.534	$128.53	$128.55	$128.50
Purchase #3	$22.77	12.242%	$25.5575	$25.56	$25.55	$25.60
Purchase #4	$205.63	11.388%	$229.0471	$229.05	$229.05	$229.00
Purchase #5	$211.56	8.674%	$229.9107	$229.91	$229.90	$229.90
Purchase #6	$126.43	13.813%	$143.8938	$143.89	$143.90	$143.90
Purchase #7	$205.72	13.863%	$234.239	$234.24	$234.25	$234.20
7 purchase totals =	$965.88		$1,081.5856	$1,081.58	$1,081.60	$1,081.50