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	$28.84	3.249%	$29.777	$29.78	$29.80	$29.80
Purchase #2	$75.79	3.405%	$78.3706	$78.37	$78.35	$78.40
Purchase #3	$250.74	13.591%	$284.8181	$284.82	$284.80	$284.80
Purchase #4	$164.93	13.271%	$186.8179	$186.82	$186.80	$186.80
Purchase #5	$49.72	13.592%	$56.4779	$56.48	$56.50	$56.50
Purchase #6	$244.64	12.773%	$275.8879	$275.89	$275.90	$275.90
Purchase #7	$176.99	8.386%	$191.8324	$191.83	$191.85	$191.80
7 purchase totals =	$991.65		$1,103.9818	$1,103.99	$1,104.00	$1,104.00