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	$249.99	7.372%	$268.4193	$268.42	$268.40	$268.40
Purchase #2	$48.73	11.403%	$54.2867	$54.29	$54.30	$54.30
Purchase #3	$11.39	6.330%	$12.111	$12.11	$12.10	$12.10
Purchase #4	$176.31	5.863%	$186.6471	$186.65	$186.65	$186.60
Purchase #5	$40.48	13.360%	$45.8881	$45.89	$45.90	$45.90
Purchase #6	$136.38	5.702%	$144.1564	$144.16	$144.15	$144.20
Purchase #7	$190.32	5.110%	$200.0454	$200.05	$200.05	$200.00
7 purchase totals =	$853.60		$911.5540	$911.57	$911.55	$911.50