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	$247.80	3.421%	$256.2772	$256.28	$256.30	$256.30
Purchase #2	$116.93	12.845%	$131.9497	$131.95	$131.95	$131.90
Purchase #3	$164.26	9.251%	$179.4557	$179.46	$179.45	$179.50
Purchase #4	$197.47	13.355%	$223.8421	$223.84	$223.85	$223.80
Purchase #5	$134.72	7.474%	$144.789	$144.79	$144.80	$144.80
Purchase #6	$219.75	5.138%	$231.0408	$231.04	$231.05	$231.00
Purchase #7	$200.80	7.378%	$215.615	$215.62	$215.60	$215.60
7 purchase totals =	$1,281.73		$1,382.9695	$1,382.98	$1,383.00	$1,382.90