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	$8.49	4.421%	$8.8653	$8.87	$8.85	$8.90
Purchase #2	$176.41	7.307%	$189.3003	$189.30	$189.30	$189.30
Purchase #3	$121.94	7.610%	$131.2196	$131.22	$131.20	$131.20
Purchase #4	$241.58	11.261%	$268.7843	$268.78	$268.80	$268.80
Purchase #5	$107.82	3.507%	$111.6012	$111.60	$111.60	$111.60
Purchase #6	$105.36	5.636%	$111.2981	$111.30	$111.30	$111.30
Purchase #7	$26.48	6.811%	$28.2836	$28.28	$28.30	$28.30
7 purchase totals =	$788.08		$849.3524	$849.35	$849.35	$849.40