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	$18.32	13.292%	$20.7551	$20.76	$20.75	$20.80
Purchase #2	$35.59	8.257%	$38.5287	$38.53	$38.55	$38.50
Purchase #3	$102.25	9.859%	$112.3308	$112.33	$112.35	$112.30
Purchase #4	$155.83	6.494%	$165.9496	$165.95	$165.95	$165.90
Purchase #5	$148.45	10.533%	$164.0862	$164.09	$164.10	$164.10
Purchase #6	$237.33	12.324%	$266.5785	$266.58	$266.60	$266.60
Purchase #7	$54.40	11.258%	$60.5244	$60.52	$60.50	$60.50
7 purchase totals =	$752.17		$828.7533	$828.76	$828.80	$828.70