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	$124.67	3.390%	$128.8963	$128.90	$128.90	$128.90
Purchase #2	$54.60	9.380%	$59.7215	$59.72	$59.70	$59.70
Purchase #3	$225.83	7.524%	$242.8214	$242.82	$242.80	$242.80
Purchase #4	$242.61	6.791%	$259.0856	$259.09	$259.10	$259.10
Purchase #5	$228.52	6.104%	$242.4689	$242.47	$242.45	$242.50
Purchase #6	$118.36	9.460%	$129.5569	$129.56	$129.55	$129.60
Purchase #7	$162.69	13.335%	$184.3847	$184.38	$184.40	$184.40
7 purchase totals =	$1,157.28		$1,246.9353	$1,246.94	$1,246.90	$1,247.00