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	$52.50	6.181%	$55.745	$55.75	$55.75	$55.70
Purchase #2	$116.34	6.482%	$123.8812	$123.88	$123.90	$123.90
Purchase #3	$9.38	13.137%	$10.6123	$10.61	$10.60	$10.60
Purchase #4	$31.72	9.459%	$34.7204	$34.72	$34.70	$34.70
Purchase #5	$53.98	6.725%	$57.6102	$57.61	$57.60	$57.60
Purchase #6	$161.34	5.786%	$170.6751	$170.68	$170.70	$170.70
Purchase #7	$112.57	5.766%	$119.0608	$119.06	$119.05	$119.10
7 purchase totals =	$537.83		$572.3050	$572.31	$572.30	$572.30