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	$82.47	8.854%	$89.7719	$89.77	$89.75	$89.80
Purchase #2	$55.45	5.179%	$58.3218	$58.32	$58.30	$58.30
Purchase #3	$127.49	11.582%	$142.2559	$142.26	$142.25	$142.30
Purchase #4	$136.35	9.142%	$148.8151	$148.82	$148.80	$148.80
Purchase #5	$82.61	4.630%	$86.4348	$86.43	$86.45	$86.40
Purchase #6	$75.92	9.406%	$83.061	$83.06	$83.05	$83.10
Purchase #7	$245.42	5.321%	$258.4788	$258.48	$258.50	$258.50
7 purchase totals =	$805.71		$867.1393	$867.14	$867.10	$867.20