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	$142.76	12.595%	$160.7406	$160.74	$160.75	$160.70
Purchase #2	$5.89	13.593%	$6.6906	$6.69	$6.70	$6.70
Purchase #3	$91.27	9.724%	$100.1451	$100.15	$100.15	$100.10
Purchase #4	$63.68	7.529%	$68.4745	$68.47	$68.45	$68.50
Purchase #5	$84.88	5.608%	$89.6401	$89.64	$89.65	$89.60
Purchase #6	$240.52	3.240%	$248.3128	$248.31	$248.30	$248.30
Purchase #7	$108.56	7.696%	$116.9148	$116.91	$116.90	$116.90
7 purchase totals =	$737.56		$790.9185	$790.91	$790.90	$790.80