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	$233.69	6.810%	$249.6043	$249.60	$249.60	$249.60
Purchase #2	$127.68	12.723%	$143.9247	$143.92	$143.90	$143.90
Purchase #3	$236.82	3.577%	$245.2911	$245.29	$245.30	$245.30
Purchase #4	$66.38	11.485%	$74.0037	$74.00	$74.00	$74.00
Purchase #5	$60.39	4.143%	$62.892	$62.89	$62.90	$62.90
Purchase #6	$95.96	4.143%	$99.9356	$99.94	$99.95	$99.90
Purchase #7	$178.87	6.164%	$189.8955	$189.90	$189.90	$189.90
7 purchase totals =	$999.79		$1,065.5469	$1,065.54	$1,065.55	$1,065.50