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	$132.80	7.469%	$142.7188	$142.72	$142.70	$142.70
Purchase #2	$128.37	8.606%	$139.4175	$139.42	$139.40	$139.40
Purchase #3	$167.97	13.261%	$190.2445	$190.24	$190.25	$190.20
Purchase #4	$34.49	7.606%	$37.1133	$37.11	$37.10	$37.10
Purchase #5	$102.30	9.446%	$111.9633	$111.96	$111.95	$112.00
Purchase #6	$94.29	11.765%	$105.3832	$105.38	$105.40	$105.40
Purchase #7	$105.99	4.784%	$111.0606	$111.06	$111.05	$111.10
7 purchase totals =	$766.21		$837.9012	$837.89	$837.85	$837.90