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	$38.31	11.400%	$42.6773	$42.68	$42.70	$42.70
Purchase #2	$58.91	5.201%	$61.9739	$61.97	$61.95	$62.00
Purchase #3	$205.25	12.677%	$231.2695	$231.27	$231.25	$231.30
Purchase #4	$42.40	13.370%	$48.0689	$48.07	$48.05	$48.10
Purchase #5	$245.75	13.527%	$278.9926	$278.99	$279.00	$279.00
Purchase #6	$187.77	4.590%	$196.3886	$196.39	$196.40	$196.40
Purchase #7	$101.93	7.649%	$109.7266	$109.73	$109.75	$109.70
7 purchase totals =	$880.32		$969.0974	$969.10	$969.10	$969.20