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	$222.44	4.862%	$233.255	$233.26	$233.25	$233.30
Purchase #2	$164.35	9.803%	$180.4612	$180.46	$180.45	$180.50
Purchase #3	$247.88	13.301%	$280.8505	$280.85	$280.85	$280.90
Purchase #4	$133.47	9.493%	$146.1403	$146.14	$146.15	$146.10
Purchase #5	$225.98	3.686%	$234.3096	$234.31	$234.30	$234.30
Purchase #6	$12.63	7.541%	$13.5824	$13.58	$13.60	$13.60
Purchase #7	$171.70	11.113%	$190.781	$190.78	$190.80	$190.80
7 purchase totals =	$1,178.45		$1,279.3800	$1,279.38	$1,279.40	$1,279.50