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	$34.98	11.402%	$38.9684	$38.97	$38.95	$39.00
Purchase #2	$13.81	5.292%	$14.5408	$14.54	$14.55	$14.50
Purchase #3	$154.93	6.473%	$164.9586	$164.96	$164.95	$165.00
Purchase #4	$131.45	13.228%	$148.8382	$148.84	$148.85	$148.80
Purchase #5	$40.59	4.152%	$42.2753	$42.28	$42.30	$42.30
Purchase #6	$49.66	12.540%	$55.8874	$55.89	$55.90	$55.90
Purchase #7	$72.31	10.369%	$79.8078	$79.81	$79.80	$79.80
7 purchase totals =	$497.73		$545.2765	$545.29	$545.30	$545.30