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	$170.46	8.288%	$184.5877	$184.59	$184.60	$184.60
Purchase #2	$202.89	11.132%	$225.4757	$225.48	$225.50	$225.50
Purchase #3	$238.95	13.450%	$271.0888	$271.09	$271.10	$271.10
Purchase #4	$198.98	11.783%	$222.4258	$222.43	$222.45	$222.40
Purchase #5	$87.46	11.225%	$97.2774	$97.28	$97.30	$97.30
Purchase #6	$222.46	4.870%	$233.2938	$233.29	$233.30	$233.30
Purchase #7	$41.31	12.461%	$46.4576	$46.46	$46.45	$46.50
7 purchase totals =	$1,162.51		$1,280.6068	$1,280.62	$1,280.70	$1,280.70