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	$13.35	6.113%	$14.1661	$14.17	$14.15	$14.20
Purchase #2	$175.63	6.750%	$187.485	$187.49	$187.50	$187.50
Purchase #3	$243.54	10.114%	$268.1716	$268.17	$268.15	$268.20
Purchase #4	$11.40	11.257%	$12.6833	$12.68	$12.70	$12.70
Purchase #5	$146.59	12.418%	$164.7935	$164.79	$164.80	$164.80
Purchase #6	$40.82	6.123%	$43.3194	$43.32	$43.30	$43.30
Purchase #7	$238.50	4.729%	$249.7787	$249.78	$249.80	$249.80
7 purchase totals =	$869.83		$940.3976	$940.40	$940.40	$940.50