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	$160.45	3.393%	$165.8941	$165.89	$165.90	$165.90
Purchase #2	$89.35	4.328%	$93.2171	$93.22	$93.20	$93.20
Purchase #3	$220.74	6.491%	$235.0682	$235.07	$235.05	$235.10
Purchase #4	$132.82	6.825%	$141.885	$141.89	$141.90	$141.90
Purchase #5	$164.43	7.194%	$176.2591	$176.26	$176.25	$176.30
Purchase #6	$200.79	7.138%	$215.1224	$215.12	$215.10	$215.10
Purchase #7	$247.31	3.347%	$255.5875	$255.59	$255.60	$255.60
7 purchase totals =	$1,215.89		$1,283.0334	$1,283.04	$1,283.00	$1,283.10