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	$27.88	10.441%	$30.791	$30.79	$30.80	$30.80
Purchase #2	$53.52	11.804%	$59.8375	$59.84	$59.85	$59.80
Purchase #3	$116.78	12.370%	$131.2257	$131.23	$131.25	$131.20
Purchase #4	$132.53	13.660%	$150.6336	$150.63	$150.65	$150.60
Purchase #5	$52.40	5.332%	$55.194	$55.19	$55.20	$55.20
Purchase #6	$248.25	12.506%	$279.2961	$279.30	$279.30	$279.30
Purchase #7	$100.99	7.381%	$108.4441	$108.44	$108.45	$108.40
7 purchase totals =	$732.35		$815.4220	$815.42	$815.50	$815.30