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	$83.96	6.421%	$89.3511	$89.35	$89.35	$89.40
Purchase #2	$64.80	9.790%	$71.1439	$71.14	$71.15	$71.10
Purchase #3	$209.55	12.837%	$236.4499	$236.45	$236.45	$236.40
Purchase #4	$88.25	12.206%	$99.0218	$99.02	$99.00	$99.00
Purchase #5	$172.87	3.144%	$178.305	$178.31	$178.30	$178.30
Purchase #6	$116.54	5.593%	$123.0581	$123.06	$123.05	$123.10
Purchase #7	$107.30	3.582%	$111.1435	$111.14	$111.15	$111.10
7 purchase totals =	$843.27		$908.4733	$908.47	$908.45	$908.40