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	$70.60	12.539%	$79.4525	$79.45	$79.45	$79.50
Purchase #2	$168.39	7.764%	$181.4638	$181.46	$181.45	$181.50
Purchase #3	$146.37	8.300%	$158.5187	$158.52	$158.50	$158.50
Purchase #4	$174.29	5.531%	$183.93	$183.93	$183.95	$183.90
Purchase #5	$126.84	12.359%	$142.5162	$142.52	$142.50	$142.50
Purchase #6	$194.76	12.608%	$219.3153	$219.32	$219.30	$219.30
Purchase #7	$117.43	8.233%	$127.098	$127.10	$127.10	$127.10
7 purchase totals =	$998.68		$1,092.2945	$1,092.30	$1,092.25	$1,092.30