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	$6.74	6.592%	$7.1843	$7.18	$7.20	$7.20
Purchase #2	$50.61	10.806%	$56.0789	$56.08	$56.10	$56.10
Purchase #3	$112.98	8.221%	$122.2681	$122.27	$122.25	$122.30
Purchase #4	$42.32	3.542%	$43.819	$43.82	$43.80	$43.80
Purchase #5	$207.39	6.806%	$221.505	$221.51	$221.50	$221.50
Purchase #6	$86.64	3.771%	$89.9072	$89.91	$89.90	$89.90
Purchase #7	$131.52	12.164%	$147.5181	$147.52	$147.50	$147.50
7 purchase totals =	$638.20		$688.2806	$688.29	$688.25	$688.30