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	$231.54	10.443%	$255.7197	$255.72	$255.70	$255.70
Purchase #2	$82.87	7.840%	$89.367	$89.37	$89.35	$89.40
Purchase #3	$221.45	12.181%	$248.4248	$248.42	$248.40	$248.40
Purchase #4	$133.49	7.779%	$143.8742	$143.87	$143.85	$143.90
Purchase #5	$197.31	3.448%	$204.1132	$204.11	$204.10	$204.10
Purchase #6	$12.32	11.716%	$13.7634	$13.76	$13.75	$13.80
Purchase #7	$89.66	13.444%	$101.7139	$101.71	$101.70	$101.70
7 purchase totals =	$968.64		$1,056.9762	$1,056.96	$1,056.85	$1,057.00