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	$186.43	11.778%	$208.3877	$208.39	$208.40	$208.40
Purchase #2	$158.60	4.551%	$165.8179	$165.82	$165.80	$165.80
Purchase #3	$225.90	3.714%	$234.2899	$234.29	$234.30	$234.30
Purchase #4	$61.62	12.844%	$69.5345	$69.53	$69.55	$69.50
Purchase #5	$35.86	5.493%	$37.8298	$37.83	$37.85	$37.80
Purchase #6	$127.69	11.774%	$142.7242	$142.72	$142.70	$142.70
Purchase #7	$248.75	6.552%	$265.0481	$265.05	$265.05	$265.00
7 purchase totals =	$1,044.85		$1,123.6321	$1,123.63	$1,123.65	$1,123.50