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	$132.83	12.547%	$149.4962	$149.50	$149.50	$149.50
Purchase #2	$19.80	5.319%	$20.8532	$20.85	$20.85	$20.90
Purchase #3	$190.82	13.139%	$215.8918	$215.89	$215.90	$215.90
Purchase #4	$23.53	12.490%	$26.4689	$26.47	$26.45	$26.50
Purchase #5	$223.86	12.127%	$251.0075	$251.01	$251.00	$251.00
Purchase #6	$47.76	9.829%	$52.4543	$52.45	$52.45	$52.50
Purchase #7	$84.26	6.209%	$89.4917	$89.49	$89.50	$89.50
7 purchase totals =	$722.86		$805.6636	$805.66	$805.65	$805.80