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	$72.82	11.591%	$81.2606	$81.26	$81.25	$81.30
Purchase #2	$112.78	13.685%	$128.2139	$128.21	$128.20	$128.20
Purchase #3	$232.89	6.519%	$248.0721	$248.07	$248.05	$248.10
Purchase #4	$148.80	10.853%	$164.9493	$164.95	$164.95	$164.90
Purchase #5	$115.98	9.569%	$127.0781	$127.08	$127.10	$127.10
Purchase #6	$16.47	11.120%	$18.3015	$18.30	$18.30	$18.30
Purchase #7	$101.99	9.675%	$111.8575	$111.86	$111.85	$111.90
7 purchase totals =	$801.73		$879.7330	$879.73	$879.70	$879.80