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	$60.63	11.279%	$67.4685	$67.47	$67.45	$67.50
Purchase #2	$122.96	13.422%	$139.4637	$139.46	$139.45	$139.50
Purchase #3	$126.93	7.874%	$136.9245	$136.92	$136.90	$136.90
Purchase #4	$127.98	11.845%	$143.1392	$143.14	$143.15	$143.10
Purchase #5	$70.38	3.220%	$72.6462	$72.65	$72.65	$72.60
Purchase #6	$198.75	12.180%	$222.9578	$222.96	$222.95	$223.00
Purchase #7	$205.49	8.670%	$223.306	$223.31	$223.30	$223.30
7 purchase totals =	$913.12		$1,005.9059	$1,005.91	$1,005.85	$1,005.90