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	$81.86	9.825%	$89.9027	$89.90	$89.90	$89.90
Purchase #2	$175.47	6.348%	$186.6088	$186.61	$186.60	$186.60
Purchase #3	$118.86	7.685%	$127.9944	$127.99	$128.00	$128.00
Purchase #4	$9.72	3.322%	$10.0429	$10.04	$10.05	$10.00
Purchase #5	$65.26	11.402%	$72.7009	$72.70	$72.70	$72.70
Purchase #6	$74.71	5.428%	$78.7653	$78.77	$78.75	$78.80
Purchase #7	$124.60	13.518%	$141.4434	$141.44	$141.45	$141.40
7 purchase totals =	$650.48		$707.4584	$707.45	$707.45	$707.40