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	$29.73	13.818%	$33.8381	$33.84	$33.85	$33.80
Purchase #2	$214.93	3.441%	$222.3257	$222.33	$222.35	$222.30
Purchase #3	$176.87	13.411%	$200.59	$200.59	$200.60	$200.60
Purchase #4	$122.66	7.472%	$131.8252	$131.83	$131.85	$131.80
Purchase #5	$120.98	5.382%	$127.4911	$127.49	$127.50	$127.50
Purchase #6	$136.26	11.443%	$151.8522	$151.85	$151.85	$151.90
Purchase #7	$225.65	11.585%	$251.7916	$251.79	$251.80	$251.80
7 purchase totals =	$1,027.08		$1,119.7139	$1,119.72	$1,119.80	$1,119.70