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	$32.40	7.337%	$34.7772	$34.78	$34.80	$34.80
Purchase #2	$211.57	11.230%	$235.3293	$235.33	$235.35	$235.30
Purchase #3	$63.75	6.331%	$67.786	$67.79	$67.80	$67.80
Purchase #4	$136.62	4.768%	$143.134	$143.13	$143.15	$143.10
Purchase #5	$164.94	10.262%	$181.8661	$181.87	$181.85	$181.90
Purchase #6	$91.56	9.526%	$100.282	$100.28	$100.30	$100.30
Purchase #7	$111.93	3.678%	$116.0468	$116.05	$116.05	$116.00
7 purchase totals =	$812.77		$879.2214	$879.23	$879.30	$879.20