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	$248.77	11.724%	$277.9358	$277.94	$277.95	$277.90
Purchase #2	$202.51	10.628%	$224.0328	$224.03	$224.05	$224.00
Purchase #3	$182.72	8.595%	$198.4248	$198.42	$198.40	$198.40
Purchase #4	$123.27	4.256%	$128.5164	$128.52	$128.50	$128.50
Purchase #5	$143.71	9.529%	$157.4041	$157.40	$157.40	$157.40
Purchase #6	$78.82	13.824%	$89.7161	$89.72	$89.70	$89.70
Purchase #7	$100.95	8.280%	$109.3087	$109.31	$109.30	$109.30
7 purchase totals =	$1,080.75		$1,185.3387	$1,185.34	$1,185.30	$1,185.20