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	$170.97	5.826%	$180.9307	$180.93	$180.95	$180.90
Purchase #2	$43.51	4.595%	$45.5093	$45.51	$45.50	$45.50
Purchase #3	$187.90	10.602%	$207.8212	$207.82	$207.80	$207.80
Purchase #4	$140.45	11.499%	$156.6003	$156.60	$156.60	$156.60
Purchase #5	$46.74	4.271%	$48.7363	$48.74	$48.75	$48.70
Purchase #6	$19.36	13.114%	$21.8989	$21.90	$21.90	$21.90
Purchase #7	$148.90	11.742%	$166.3838	$166.38	$166.40	$166.40
7 purchase totals =	$757.83		$827.8805	$827.88	$827.90	$827.80