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	$66.67	10.257%	$73.5083	$73.51	$73.50	$73.50
Purchase #2	$161.91	13.585%	$183.9055	$183.91	$183.90	$183.90
Purchase #3	$55.93	8.155%	$60.4911	$60.49	$60.50	$60.50
Purchase #4	$180.94	5.586%	$191.0473	$191.05	$191.05	$191.00
Purchase #5	$19.59	9.839%	$21.5175	$21.52	$21.50	$21.50
Purchase #6	$171.62	6.652%	$183.0362	$183.04	$183.05	$183.00
Purchase #7	$54.95	7.540%	$59.0932	$59.09	$59.10	$59.10
7 purchase totals =	$711.61		$772.5991	$772.61	$772.60	$772.50