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	$250.31	6.455%	$266.4675	$266.47	$266.45	$266.50
Purchase #2	$243.80	10.261%	$268.8163	$268.82	$268.80	$268.80
Purchase #3	$97.70	3.266%	$100.8909	$100.89	$100.90	$100.90
Purchase #4	$180.90	13.609%	$205.5187	$205.52	$205.50	$205.50
Purchase #5	$234.91	7.440%	$252.3873	$252.39	$252.40	$252.40
Purchase #6	$207.64	4.756%	$217.5154	$217.52	$217.50	$217.50
Purchase #7	$231.25	13.846%	$263.2689	$263.27	$263.25	$263.30
7 purchase totals =	$1,446.51		$1,574.8650	$1,574.88	$1,574.80	$1,574.90