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	$248.46	12.442%	$279.3734	$279.37	$279.35	$279.40
Purchase #2	$116.90	10.303%	$128.9442	$128.94	$128.95	$128.90
Purchase #3	$26.86	4.495%	$28.0674	$28.07	$28.05	$28.10
Purchase #4	$234.30	8.301%	$253.7492	$253.75	$253.75	$253.70
Purchase #5	$124.85	5.493%	$131.708	$131.71	$131.70	$131.70
Purchase #6	$110.49	12.717%	$124.541	$124.54	$124.55	$124.50
Purchase #7	$64.56	8.477%	$70.0328	$70.03	$70.05	$70.00
7 purchase totals =	$926.42		$1,016.4160	$1,016.41	$1,016.40	$1,016.30