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	$17.60	4.714%	$18.4297	$18.43	$18.45	$18.40
Purchase #2	$247.95	11.148%	$275.5915	$275.59	$275.60	$275.60
Purchase #3	$103.78	5.561%	$109.5512	$109.55	$109.55	$109.60
Purchase #4	$191.38	12.408%	$215.1264	$215.13	$215.15	$215.10
Purchase #5	$182.59	4.533%	$190.8668	$190.87	$190.85	$190.90
Purchase #6	$74.67	5.160%	$78.523	$78.52	$78.50	$78.50
Purchase #7	$94.85	5.553%	$100.117	$100.12	$100.10	$100.10
7 purchase totals =	$912.82		$988.2056	$988.21	$988.20	$988.20