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	$72.31	8.591%	$78.5222	$78.52	$78.50	$78.50
Purchase #2	$224.27	13.286%	$254.0665	$254.07	$254.05	$254.10
Purchase #3	$25.35	8.726%	$27.562	$27.56	$27.55	$27.60
Purchase #4	$36.41	4.468%	$38.0368	$38.04	$38.05	$38.00
Purchase #5	$93.28	13.591%	$105.9577	$105.96	$105.95	$106.00
Purchase #6	$248.81	5.337%	$262.089	$262.09	$262.10	$262.10
Purchase #7	$188.88	12.488%	$212.4673	$212.47	$212.45	$212.50
7 purchase totals =	$889.31		$978.7015	$978.71	$978.65	$978.80