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	$148.64	5.284%	$156.4941	$156.49	$156.50	$156.50
Purchase #2	$54.79	8.612%	$59.5085	$59.51	$59.50	$59.50
Purchase #3	$60.83	10.681%	$67.3273	$67.33	$67.35	$67.30
Purchase #4	$45.44	6.861%	$48.5576	$48.56	$48.55	$48.60
Purchase #5	$38.93	5.147%	$40.9337	$40.93	$40.95	$40.90
Purchase #6	$215.81	5.390%	$227.4422	$227.44	$227.45	$227.40
Purchase #7	$100.84	4.461%	$105.3385	$105.34	$105.35	$105.30
7 purchase totals =	$665.28		$705.6019	$705.60	$705.65	$705.50