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	$31.63	10.595%	$34.9812	$34.98	$35.00	$35.00
Purchase #2	$55.79	8.372%	$60.4607	$60.46	$60.45	$60.50
Purchase #3	$233.28	9.345%	$255.08	$255.08	$255.10	$255.10
Purchase #4	$113.37	10.708%	$125.5097	$125.51	$125.50	$125.50
Purchase #5	$96.98	6.661%	$103.4398	$103.44	$103.45	$103.40
Purchase #6	$118.47	4.525%	$123.8308	$123.83	$123.85	$123.80
Purchase #7	$180.86	10.500%	$199.8503	$199.85	$199.85	$199.90
7 purchase totals =	$830.38		$903.1525	$903.15	$903.20	$903.20