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	$12.80	8.644%	$13.9064	$13.91	$13.90	$13.90
Purchase #2	$66.57	9.257%	$72.7324	$72.73	$72.75	$72.70
Purchase #3	$39.72	9.640%	$43.549	$43.55	$43.55	$43.50
Purchase #4	$238.38	13.685%	$271.0023	$271.00	$271.00	$271.00
Purchase #5	$122.27	12.813%	$137.9365	$137.94	$137.95	$137.90
Purchase #6	$129.83	12.317%	$145.8212	$145.82	$145.80	$145.80
Purchase #7	$150.27	9.153%	$164.0242	$164.02	$164.00	$164.00
7 purchase totals =	$759.84		$848.9720	$848.97	$848.95	$848.80