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	$167.40	7.104%	$179.2921	$179.29	$179.30	$179.30
Purchase #2	$96.92	12.548%	$109.0815	$109.08	$109.10	$109.10
Purchase #3	$193.26	7.507%	$207.768	$207.77	$207.75	$207.80
Purchase #4	$43.70	4.157%	$45.5166	$45.52	$45.50	$45.50
Purchase #5	$228.85	12.376%	$257.1725	$257.17	$257.15	$257.20
Purchase #6	$54.57	9.107%	$59.5397	$59.54	$59.55	$59.50
Purchase #7	$107.56	4.579%	$112.4852	$112.49	$112.50	$112.50
7 purchase totals =	$892.26		$970.8556	$970.86	$970.85	$970.90